# Monitoring Immunotherapy in Veterinary Oncology: Response and Toxicity ## Key Takeaways - Immunotherapy response assessment requires adapted criteria (e.g., iRECIST) due to delayed responses and potential for transient lesion enlargement (pseudoprogression), necessitating confirmatory imaging 4-8 weeks after initial re-evaluation if progression is suspected. - Immune-related adverse events (irAEs) like dermatitis, colitis, hepatitis, pneumonitis, and endocrinopathies arise from immune activation, not direct cellular injury, and are graded using adapted VCOG-CTCAE criteria, with immunosuppressive doses of corticosteroids being first-line for grade 3 or 4 toxicity. - Baseline assessment must include comprehensive staging (radiography, ultrasound, lymph node evaluation), organ function (CBC, biochemistry, urinalysis), and endocrine screening (thyroid hormone) to establish reference points for monitoring irAEs. - Laboratory monitoring should include serial CBCs and biochemistry panels before each cycle during induction, with specific attention to lymphocyte counts, liver enzymes, creatinine, and amylase/lipase, alongside endocrine surveillance for hypothyroidism, hypoadrenocorticism, and diabetes mellitus. - Physical examinations should meticulously assess palpable lymph nodes, cutaneous lesions, and injection sites, measuring lesions in two dimensions with calipers at each visit, while client communication should proactively address the possibility of pseudoprogression to prevent premature treatment discontinuation. - The canine gut microbiome is recognized as a potential modifier of immunotherapy response, with antibiotic use during treatment advised to be minimized due to potential depletion of commensal bacteria supporting anti-tumor immunity, though fecal sampling for analysis is not yet standard clinical practice. --- Immunotherapy has expanded the treatment options available for canine and feline cancer patients, yet its monitoring demands differ fundamentally from conventional cytotoxic chemotherapy. Tumor response may lag behind treatment initiation, can present as transient worsening before improvement, and toxicity often arises from immune activation instead of direct cellular injury. This article provides a structured framework for veterinary students and practitioners who need to distinguish true progression from pseudoprogression, recognize immune-related adverse events early, and apply response criteria that were designed for the kinetics of biologic therapy. The clinical question this reference addresses is practical: which physical examinations, imaging intervals, laboratory panels, and client communication points constitute a defensible monitoring protocol for a dog or cat receiving cancer immunotherapy? The answer draws on comparative oncology literature, human immune oncology response criteria adapted for veterinary use, and the emerging recognition that tumor-associated inflammation can confound conventional imaging interpretation. Species differences between dogs and cats are highlighted where they alter monitoring decisions. ## At a Glance | Parameter | Monitoring Consideration | |---|---| | Response assessment timing | Conventional RECIST-style intervals may misclassify delayed responses, schedule first re-evaluation at 8 to 12 weeks where feasible | | Pseudoprogression | Transient increase in lesion size or new lesions from immune cell infiltration, requires biopsy or short-interval imaging before declaring progression | | Physical examination | Palpable lymph nodes, cutaneous lesions, and injection sites at each visit, measure with calipers in two dimensions | | Laboratory monitoring | Complete blood count, biochemistry panel, and urinalysis at baseline and each cycle, add specific panels when organ-specific immune toxicity is suspected | | Immune-related adverse events | Dermatitis, colitis, hepatitis, pneumonitis, endocrinopathies, and polyarthritis, grade by adapted VCOG-CTCAE criteria | | Corticosteroid use | Do not assume steroids negate antitumour immunity, immunosuppressive doses are first-line for most grade 3 or 4 immune toxicity | | Microbiome status | Gut microbial composition may influence checkpoint inhibitor response, fecal sampling is research-grade, not yet standard clinical monitoring | ## Conceptual Basis of Immunotherapy Monitoring ### Tumor-Immune Dynamics and the Inflammatory Microenvironment The inflammatory response, mediated by tissue-resident or newly recruited macrophages, is an underlying pathophysiological condition for many diseases, including cancer. Paradoxically, inflammation is a double-edged sword in oncology. For many solid tumors, high density of cells expressing macrophage-associated markers is associated with poor clinical outcome, characterized by an inflamed microenvironment, a high level of dissemination, and resistance to conventional chemotherapies. Radiation treatment also triggers an inflammatory response in tumors, often referred to as pseudoprogression, which can be associated with a positive treatment response. Non-invasive imaging of cancer inflammation and tumor-associated macrophages therefore provides a diagnostic tool and monitoring strategy for immuno- and radiotherapies, as described in the institutional review of nanoparticle-based magnetic resonance imaging of tumor-associated macrophages and inflammation by Serkova (2017). Quantitative T2-weighted MRI using superparamagnetic iron oxide nanoparticles has been reported for assessment of tumor-associated macrophages in animal models and human trials. This inflammatory biology explains why immunotherapy response does not follow the monotonic shrinkage expected from cytotoxic drugs. Immune effector cells, edema, and granulation tissue can enlarge a lesion before tumor cell death becomes radiographically evident. A monitoring protocol that treats any size increase as treatment failure will prematurely discontinue therapy that might otherwise produce durable remission. ### Comparative Oncology and the Canine Model Dogs with spontaneous cancers, including lymphoma, high-grade glioma, melanoma, and osteosarcoma, closely resemble their human analogues in metastasis, disease recurrence, and response to treatment. These dogs also have intact immune systems, which supports the translational value of microbiome analyzes in the setting of novel immunotherapy, as reviewed by Kleber and colleagues in their discussion of the canine microbiome and cancer immunotherapy (2022). The gut microbiome has been established as a field of interest in tumor immunology, with growing evidence supporting its role in immune surveillance, self-tolerance, and response to immune checkpoint inhibitors. Studies using fecal microbial transplantation have demonstrated that response to checkpoint immunotherapies may be conferred or eliminated through gut microbiome modulation. While the exact mechanisms remain incompletely understood, and mouse and human gut microbiome composition may be too dissimilar for discovery of all relevant biomarkers, the dog offers a high-yield comparative model. For the monitoring clinician, this comparative framework has two consequences. First, response criteria developed in human immuno-oncology, such as iRECIST, provide a rational starting point for veterinary adaptation. Second, the microbiome represents a potential modifier of response that is not captured by conventional staging. Routine fecal sampling is not yet standard practice, but the clinician should recognize that antibiotic use during immunotherapy may carry immunologic consequences that are not yet fully characterized. ### Allergic Inflammation and Tumor Biology The relationship between allergic disease and cancer prognosis has been explored in the field of AllergoOncology. Allergic disease stems from a Th2-biased immune response to allergens in predisposed atopic individuals, and allergic disorders vary in phenotype, genotype, and endotype. The joint EAACI-EANO position paper on biomarkers and refined classification in the allergy and glioma nexus summarizes evidence that animal studies indicate allergic airway inflammation may delay glioma progression (Turner et al., 2024). Gliomas exhibit a complex tumor-immune interphase and distinct immune microenvironment features, and immunotherapy holds promise for primary brain tumor treatment but requires more specific and effective approaches. This literature informs monitoring of brain tumors in dogs and cats receiving immunotherapy. Intracranial response assessment is complicated by the blood-brain barrier, peritumoural edema, and the difficulty of distinguishing treatment-related inflammation from tumor growth. The position paper's emphasis on molecular biomarkers for glioma subtyping suggests that histopathologic and molecular characterization at diagnosis will increasingly guide both treatment selection and the interpretation of post-treatment imaging changes. ## Response Assessment Frameworks ### Limitations of Conventional Cytotoxic Response Criteria Response Evaluation Criteria in Solid Tumors (RECIST) and the veterinary adaptation, VCOG-RECIST, were developed for cytotoxic chemotherapy, where response is expected within weeks and progression is defined by measurable growth. Immunotherapy violates several assumptions of these systems. Responses can occur after an initial increase in lesion size, new lesions can appear before regression of established disease, and stable disease can persist for months before a delayed response becomes apparent. Applying conventional criteria at early time points therefore risks misclassifying eventual responders as progressors. ### Adapted Immune Response Criteria The human immune-related response criteria (irRC) and subsequent iRECIST were developed to address these kinetics. They introduce the concept of unconfirmed progression, where a lesion increase triggers a short-interval confirmatory scan instead of immediate treatment discontinuation. Clinical decision frameworks adapted from these systems use a four- to eight-week confirmatory interval, and they require that new lesions be incorporated into total tumor burden instead of automatically defining progression. Veterinary oncology has not yet adopted a single standardized immune response criteria set, and the clinician should document which criteria are being applied in the medical record. ## Baseline Assessment Before Immunotherapy Initiation ### Staging and Tumor Burden Documentation Complete staging should precede the first immunotherapy dose. This includes three-view thoracic radiography, abdominal ultrasound, and regional lymph node evaluation for solid tumors, with advanced imaging where intracranial or spinal disease is suspected. Measurable lesions should be identified and recorded in two dimensions, with consistent imaging modality and technique across re-evaluations. Baseline biopsy material should be reviewed to confirm histologic diagnosis and, where relevant, immunophenotype or molecular markers that may predict response. ### Organ Function and Immune Status Baseline complete blood count, serum biochemistry panel, and urinalysis establish the reference against which immune-related adverse events will be judged. Thyroid hormone assessment is warranted before checkpoint inhibitor therapy, given the frequency of endocrinopathies in human patients and the difficulty of diagnosing hypothyroidism in dogs once clinical signs develop. Serologic testing for infectious disease should follow regional guidelines, as immunotherapy-related immunosuppression from subsequent corticosteroid administration may reactivate latent infections. ## Imaging Considerations in Immunotherapy Monitoring ### Pseudoprogression and Inflammatory Change The inflammatory response triggered by radiation and immunotherapy can produce imaging changes that mimic progressive disease. As noted in the Serkova review, radiation treatment triggers an inflammatory response in tumors that can be associated with a positive treatment response. Quantitative T2-weighted MRI using superparamagnetic iron oxide nanoparticles has been reported for non-invasive assessment of tumor-associated macrophages, offering a potential method to distinguish inflammatory infiltration from true tumor growth. This technique remains investigational in veterinary medicine, but the principle informs interpretation: a lesion that enlarges on conventional imaging may be inflamed instead of proliferating. ### When to Image and When to Repeat For most veterinary immunotherapy protocols, first re-imaging at eight to twelve weeks is reasonable, with earlier imaging reserved for clinical deterioration or suspected toxicity. If progression is suspected on the first re-evaluation, a confirmatory study four to six weeks later should be performed before discontinuing therapy, unless the patient's clinical status has clearly declined. The decision to continue therapy through suspected progression requires discussion with the owner, documentation of the rationale, and a predefined threshold for stopping. ## Laboratory Monitoring of Immune-Related Adverse Events Immune-related adverse events (irAEs) differ fundamentally from chemotherapy toxicities in their timing, unpredictability, and organ distribution. Whereas cytotoxic drug effects typically follow a dose-dependent nadir, irAEs can emerge weeks to months after treatment initiation, sometimes after therapy has been discontinued. This delayed onset mandates continued vigilance beyond the active treatment period. ### Hematologic and Biochemical Surveillance A complete blood count and serum biochemistry panel should be performed before each treatment cycle during the induction phase, then at progressively longer intervals during maintenance. The frequency can be relaxed to every 8 to 12 weeks once a patient has completed three consecutive cycles without significant laboratory abnormalities, provided the specific immunotherapy agent carries a low hematologic toxicity profile. Specific parameters warrant individual attention: - **Lymphocyte count and phenotype.** Absolute lymphocyte count trends may correlate with treatment activity, though interpretation is confounded by concurrent corticosteroid use and intercurrent illness. A rising lymphocyte count in a patient with stable disease may indicate immune activation, whereas a precipitous decline can signal treatment-related lymphopenia or progressive disease. - **Liver enzymes and bilirubin.** Hepatotoxicity is among the more common irAEs reported in veterinary patients receiving immune checkpoint inhibitors. Alanine aminotransferase elevation to greater than three times the upper reference limit, or any elevation accompanied by bilirubin increase, should prompt treatment interruption and a hepatic ultrasound to exclude biliary obstruction or metastatic disease. - **Creatinine and urinalysis.** Acute interstitial nephritis presents with azotaemia and often sterile pyuria or proteinuria. A urine protein-to-creatinine ratio provides a baseline for comparison if renal injury is suspected. - **Amylase and lipase.** Pancreatitis has been reported as an irAE in human oncology and should be considered in any patient on immunotherapy presenting with vomiting, cranial abdominal pain, or inappetence. ### Endocrine Surveillance Endocrinopathies represent a distinct challenge because they often present insidiously and may be irreversible. Hypothyroidism, hypoadrenocorticism, and diabetes mellitus have all been described in association with immune checkpoint blockade. Serial monitoring of total thyroxine, baseline cortisol, and blood glucose at each recheck examination is reasonable, particularly in patients receiving combination immunotherapy protocols. A patient who develops fatigue, weakness, or electrolyte disturbances consistent with hypoadrenocorticism requires an ACTH stimulation test. The clinician should not wait for classic hyperkalemia and hyponatraemia to appear before testing, as these findings may be absent in early immune-mediated adrenalitis. ## Structured Toxicity Grading and Management A standardized toxicity grading system allows consistent documentation and rational treatment decisions. The Veterinary Cooperative Oncology Group common terminology criteria for adverse events provides a framework that can be applied to immunotherapy, though it was not designed specifically for irAEs. Grade 1 toxicities are mild, asymptomatic, or minimally symptomatic and typically require no treatment modification. Grade 2 toxicities are moderate, may require symptomatic therapy, and often warrant holding the next dose until resolution. Grade 3 toxicities are severe or medically significant but not immediately life-threatening, and generally mandate treatment discontinuation. Grade 4 toxicities are life-threatening and require urgent intervention. | Toxicity Grade | Clinical Example | Recommended Action | Monitoring Interval | |---|---|---|---| | Grade 1 | Mild diarrhea, transient transaminitis | Continue treatment, symptomatic care | Routine scheduled recheck | | Grade 2 | Persistent diarrhea, moderate dermatitis | Hold next dose until resolution, consider short corticosteroid course | Weekly clinical and laboratory assessment | | Grade 3 | Colitis, hepatitis, pneumonitis | Discontinue immunotherapy, initiate immunosuppressive doses of corticosteroids | Twice weekly or hospitalization | | Grade 4 | Fulminant hepatitis, severe pneumonitis | Permanent discontinuation, aggressive supportive care | Daily or intensive care setting | Corticosteroid use in the management of irAEs requires a nuanced approach. Low to moderate doses of prednisolone (0.5 to 1 mg/kg daily) are generally considered acceptable for grade 2 toxicities and are unlikely to abrogate the antitumour immune response. Higher doses (2 mg/kg daily or greater) are reserved for grade 3 and 4 events. The clinician must weigh the risk of dampening therapeutic efficacy against the morbidity of uncontrolled immune activation. Tapering should occur over 2 to 4 weeks once clinical signs have resolved, and rapid discontinuation can precipitate recurrence. ## Response Monitoring Schedule The optimal monitoring schedule balances early detection of progression against the cost and stress of frequent rechecks. A pragmatic framework is presented below, with the understanding that individual protocols and patient factors will modify the intervals. | Time Point | Imaging | Laboratory | Physical Examination | Toxicity Review | |---|---|---|---|---| | Baseline (within 2 weeks before first dose) | CT or MRI of primary and metastatic sites | CBC, biochemistry, urinalysis, endocrine baseline | Full examination, body weight, body condition score | N/A | | Week 3 to 4 (after cycle 1) | None unless clinical concern | CBC, biochemistry | Full examination, weight | Symptom questionnaire, dermatologic inspection | | Week 6 to 8 (after cycle 2) | Repeat CT or MRI | CBC, biochemistry, endocrine screen | Full examination, weight | Symptom questionnaire | | Week 12 and every 8 to 12 weeks thereafter | Repeat imaging | CBC, biochemistry | Full examination, weight | Symptom questionnaire | | 4 to 8 weeks after treatment discontinuation | Consider repeat imaging | CBC, biochemistry, endocrine screen | Full examination | Symptom questionnaire | The schedule assumes a typical 3-week cycle. Protocols with different cycle lengths should adjust the imaging time points to correspond with every second or third cycle. Patients with bulky disease or rapidly progressive tumors may require imaging after the first cycle to confirm that treatment is not allowing unchecked growth. ## Microbiome Considerations in Monitoring Emerging evidence positions the gut microbiome as a modifier of immunotherapy response. Studies in murine models and human patients have demonstrated that response to checkpoint inhibitors can be influenced by gut microbial composition, and fecal microbial transplantation has been shown to confer or eliminate responsiveness in experimental settings. The canine gut microbiome shares functional characteriztics with the human microbiome, and dogs with spontaneous cancers such as lymphoma, melanoma, and osteosarcoma provide a translational bridge for studying these interactions. For the veterinary clinician, this has practical implications. Antibiotic use during immunotherapy should be minimized, as broad-spectrum antimicrobials may deplete commensal bacteria that support antitumour immunity. When antibiotics are unavoidable, the clinician should document the indication, duration, and agent used in the medical record. Probiotic supplementation remains an area of active investigation, and no specific product can be recommended based on current evidence. Fecal sampling for microbiome analysis is not yet a standard monitoring tool in clinical veterinary oncology, but clinicians participating in clinical trials should collect and store fecal samples according to protocol specifications. ## Documentation and Communication The medical record should capture the treatment plan, baseline tumor measurements, each toxicity event with its grade and management, and the rationale for any dose modification or treatment interruption. Serial imaging should be reviewed by the same radiologist when possible, and tumor measurements should follow the adapted response criteria described earlier in this article. Photographic documentation of cutaneous lesions and dermatologic irAEs provides objective evidence of change over time. Client communication must address the possibility of pseudoprogression before it occurs. Owners who understand that a transient increase in tumor size may represent an inflammatory response instead of treatment failure are less likely to request euthanasia during a period of apparent progression. The clinician should document that this discussion occurred and what the owner was told. Referral to [MSD Veterinary Manual](https://www.msdvetmanual.com/) resources and [AVMA practice resources](https://www.avma.org/resources-tools) can supplement owner education materials. ## When to Discontinue Immunotherapy Treatment discontinuation is appropriate when confirmed progressive disease develops, when a grade 3 or 4 irAE does not respond to immunosuppressive management, or when the owner elects to stop for quality-of-life or financial reasons. Pseudoprogression should be confirmed by biopsy or repeat imaging before declaring treatment failure, particularly in patients who are otherwise clinically stable. The [Davis-Thompson Foundation pathology resources](https://www.davisthompsonfoundation.org/) offer case material that can assist in interpreting biopsy findings from treated tumors, where inflammatory infiltrates and necrosis may mimic progressive disease. A patient who achieves a complete response may be considered for treatment holidays, though the optimal duration of maintenance therapy remains undefined. Decisions should be made on a case-by-case basis, weighing the risk of recurrence against cumulative toxicity and cost. ## Recognized Complications and Early Detection Immunotherapy failure modes differ from those of cytotoxic chemotherapy. Progressive disease remains the most common outcome, but hyperprogression, pseudoprogression, and immune-related adverse events (irAEs) each require distinct monitoring responses. Early detection depends on scheduled re-staging, serial laboratory work, and structured owner reporting between visits. Hyperprogression describes accelerated tumor growth after immunotherapy initiation. It is recognized when re-staging shows new lesions or a growth rate exceeding the pre-treatment trajectory. No validated veterinary criteria exist, so the diagnosis rests on comparing serial measurements against the documented pre-treatment doubling time. When hyperprogression is suspected, discontinue the immunotherapeutic agent and re-stage within two to three weeks to confirm the trend. Pseudoprogression, by contrast, reflects inflammatory infiltration and edema within or around the tumor instead of true growth. It is well described in human immunotherapy and has been reported in veterinary patients receiving radiation and immune-based combinations. The inflammatory response triggered by treatment can mimic progression on imaging, as noted in work on tumor-associated macrophages and inflammation [Nanoparticle-based magnetic resonance imaging on tumor-associated macrophages and inflammation](https://pubmed.ncbi.nlm.nih.gov/28588582/). Distinguishing pseudoprogression from genuine progression may require biopsy, advanced imaging, or a short interval re-check. Functional imaging and macrophage-directed contrast agents are under investigation for this purpose, but none are validated for routine veterinary use. Immune-related adverse events are detected through scheduled laboratory surveillance and owner observation. The most common irAEs in dogs and cats involve the gastrointestinal tract, skin, and endocrine organs. Early detection of endocrinopathies is particularly challenging because clinical signs are vague. Serial measurement of baseline and follow-up cortisol, thyroid hormone, and glucose concentrations is warranted in patients receiving checkpoint inhibitors. A sudden increase in liver enzyme activity or bilirubin should prompt investigation for immune-mediated hepatitis before clinical signs develop. | Observation | Likely cause | Discriminating check | |---|---|---| | New lesion at re-staging | Progressive disease | Compare growth rate with pre-treatment trajectory | | Enlarging index lesion, stable clinical status | Pseudoprogression | Short-interval re-imaging or biopsy, assess inflammatory markers | | Accelerated growth at first re-check | Hyperprogression | Confirm against pre-treatment doubling time, discontinue therapy | | Rising ALT or bilirubin | Immune-mediated hepatitis | Rule out other hepatotoxins, consider biopsy or empiric immunosuppression | | Lethargy, polyuria, polydipsia | Endocrine irAE | Cortisol, T4, glucose, and electrolyte panel | | Vomiting or diarrhea | Gastrointestinal irAE | Rule out infectious causes, grade severity and treat accordingly | ## Common Monitoring Errors and Corrective Action The most frequent error is applying cytotoxic response criteria without adjustment for immunotherapy kinetics. Lesions that enlarge before regressing may be misclassified as progressive disease, leading to premature discontinuation. Always document the pre-treatment growth rate and interpret early changes in that context. A second error is under-recognizing chronic, low-grade irAEs. Mild diarrhea or intermittent lethargy may be dismissed as unrelated, particularly in older patients with comorbidities. Serial owner questionnaires and a low threshold for laboratory investigation reduce this risk. Conversely, over-treating grade 1 irAEs with high-dose immunosuppression can abrogate the antitumour immune response. Reserve systemic immunosuppression for grade 3 or 4 events, or for grade 2 events that persist despite symptomatic management. A third error is failing to repeat baseline endocrine testing. A single pre-treatment cortisol measurement does not predict later adrenal insufficiency. Repeat testing is indicated when clinical signs emerge, and periodically during prolonged therapy. The MSD Veterinary Manual provides species-specific reference intervals and guidance on interpreting dynamic endocrine tests [MSD Veterinary Manual professional edition](https://www.msdvetmanual.com/). Finally, students and new clinicians often omit documentation of the baseline tumor burden in three dimensions. Without this, subsequent response assessment is unreliable. Record measurable lesions, their location, and the imaging modality used at baseline, and repeat using the same modality and technique. ## Evidence Limitations and Divergent Expert Opinion The veterinary immunotherapy evidence base remains limited. Most monitoring protocols are extrapolated from human oncology or from canine lymphoma and melanoma studies with small cohorts. No prospective veterinary trials have validated a specific response criteria set for immunotherapy, and the optimal timing of re-staging is not established. Expert opinion differs on whether pseudoprogression is clinically significant in dogs and cats or predominantly a human phenomenon. Some oncologists advocate routine biopsy of enlarging lesions, others rely on interval imaging to avoid unnecessary procedures. The role of the microbiome in treatment response is an active area of investigation. Canine cancers such as lymphoma, melanoma, and osteosarcoma resemble their human counterparts, and dogs with spontaneous tumors may provide high-yield data on microbiome-immunotherapy interactions [Using the canine microbiome to bridge translation of cancer immunotherapy](https://pubmed.ncbi.nlm.nih.gov/36032113/). However, no microbiome-based monitoring test is ready for clinical use, and routine fecal analysis is not currently recommended. AllergoOncology research highlights ongoing uncertainty about how allergic inflammation and Th2-biased immunity influence tumor behavior [AllergoOncology biomarkers and refined classification for the allergy and glioma nexus](https://pubmed.ncbi.nlm.nih.gov/38263898/). Whether pre-existing allergic disease affects immunotherapy response or irAE risk in veterinary patients is unknown. Clinicians should record allergic history at baseline but should not alter treatment decisions based on current evidence. ## Referral, Consultation, and Reporting Referral to a veterinary oncologist is appropriate when pseudoprogression or hyperprogression is suspected, when irAEs are grade 3 or higher, or when a patient fails to respond to first-line immunotherapy. Specialist input is also warranted for endocrine irAEs, which require dynamic testing and long-term management that general practitioners may not be equipped to provide. Laboratory consultation is indicated when immune-mediated cytopenias or coagulopathies are suspected, or when histopathology is needed to distinguish inflammation from progression. The Davis-Thompson Foundation offers pathology teaching resources and case material that can support diagnostic interpretation [Davis-Thompson Foundation veterinary pathology resources](https://www.davisthompsonfoundation.org/). Regulatory reporting obligations vary by jurisdiction. Veterinary professionals should consult their national veterinary board or professional association for local requirements. The American Veterinary Medical Association provides practice resources on adverse event reporting and professional obligations [AVMA practice resources](https://www.avma.org/resources-tools), and the World Organization for Animal Health publishes international standards relevant to veterinary biologicals and surveillance [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). Suspected unexpected adverse reactions to licensed immunotherapeutics should be reported to the manufacturer and the relevant regulatory authority. ## Frequently Asked Questions ### How Should I Monitor Immunotherapy When Advanced Imaging Is Not Available or Affordable? When CT or MRI is unavailable, rely on caliper measurement of superficial masses, thoracic radiography for pulmonary disease, and abdominal ultrasound for visceral lesions. Document three orthogonal dimensions at each visit using consistent landmarks. Serum biochemistry and hematology remain essential for detecting immune-related adverse events. Serial photography of skin lesions provides a reproducible visual record. For response decisions, apply the same percentage change thresholds used in adapted immune response criteria, but acknowledge that two-dimensional measurement underestimates volume changes. If imaging access is intermittent, schedule the first re-evaluation when pseudoprogression is most likely to occur, typically two to four weeks after initiation, so that subsequent comparisons use a stable baseline. Refer to the [MSD Veterinary Manual](https://www.msdvetmanual.com/) for species-specific guidance on physical examination findings that may indicate progression or toxicity. ### How Do Monitoring Protocols Differ Between Dogs and Cats? Dogs tolerate repeated venepuncture and imaging procedures more readily than cats, so feline monitoring schedules often require consolidation of blood collection with sedation events or scheduled rechecks. Cats are more sensitive to handling stress, which can confound physical examination findings such as heart rate and respiratory effort. Endocrine immune-related adverse events may present differently in cats, with subtle weight loss or behavioral change preceding biochemical confirmation. Feline patients also have a higher risk of injection-site reactions with some immunotherapies, warranting closer local inspection. The [AVMA practice resources](https://www.avma.org/resources-tools) provide general professional guidance on feline handling and stress reduction during clinical procedures. When a cat resists examination, prioritize the minimum dataset needed for that visit and defer non-urgent measurements instead of risking injury or incomplete assessment. ### What Minimum Dataset Should I Collect When Financial Constraints Limit Monitoring Frequency? A minimum dataset should include body weight, temperature, pulse and respiratory rates, tumor measurement where accessible, packed cell volume and total solids, a biochemistry panel covering liver enzymes, bilirubin, creatinine, and glucose, and a urinalysis when endocrine toxicity is suspected. This combination detects most grade 1 and 2 immune-related adverse events that require intervention. If only one blood sample is possible, run a complete blood count and a biochemistry panel with bile acids if hepatic toxicity is a concern. Client communication should address which toxicities cannot be excluded with limited testing, particularly hypoadrenocorticism and pancreatitis. Document the monitoring limitation in the medical record so that subsequent clinicians understand the diagnostic certainty of the assessments performed. The [Davis-Thompson Foundation](https://www.davisthompsonfoundation.org/) offers pathology resources that can help interpret cytology or histopathology when tissue sampling is feasible. ### How Should I Document Immunotherapy Response in the Medical Record? Record the immunotherapy agent, lot number, dose, route, and administration date for every treatment. Use a standardized toxicity grading scale and document the grade, date of onset, intervention, and resolution date for each adverse event. Tumor measurements should include the imaging modality, anatomical location, and the specific criteria applied. Note any concurrent medications, particularly corticosteroids or other immunosuppressants, because they may influence both response and toxicity interpretation. Include a subjective performance score and owner-reported quality of life assessment at each visit. Photographs should be labelled with the date and patient identifier. If the patient is enrolled in a clinical trial, follow the sponsor-specific case report form requirements. Consistent documentation supports retrospective analysis and facilitates referral if a second opinion is needed. ### How Do I Explain Pseudoprogression to an Owner Who Sees Tumor Growth on a Recheck Scan? Explain that the immune system is recruiting inflammatory cells into the tumor, which can make it appear larger on imaging even when the treatment is working. Use the analogy of swelling around a healing wound. Describe the monitoring plan: continued treatment with a short-interval recheck, typically two to four weeks later, to determine whether the lesion stabilizes or regresses. Acknowledge the owner's concern directly and state that distinguishing pseudoprogression from true progression sometimes requires time. The inflammatory response to treatment is a recognized phenomenon in immunotherapy monitoring, and tumor-associated macrophages can contribute to imaging changes that mimic progression. If the lesion continues to enlarge beyond the recheck interval or new lesions appear, true progression becomes more likely and treatment discontinuation should be discussed. ### When Should I Seek Specialist Consultation During Immunotherapy Monitoring? Consult a veterinary oncologist when a patient develops grade 3 or 4 immune-related adverse events, when suspected pseudoprogression creates diagnostic uncertainty, or when a patient fails to respond after two consecutive recheck evaluations. Early consultation is also warranted for endocrine toxicities such as suspected hypoadrenocorticism, because diagnostic confirmation and long-term management require specialised laboratory testing and treatment planning. If the patient is enrolled in a clinical trial, the study coordinator must be notified of any serious adverse event within the protocol-specified timeframe. For patients with spontaneous tumors that resemble human analogues, such as melanoma or osteosarcoma, comparative oncology resources may inform monitoring decisions. The [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) apply when immunotherapy involves biological products with potential trade or public health implications, and local veterinary authorities should be consulted in those circumstances. ## Related Clinical & Scientific Guides * [Hypersensitivity Reactions: Types and Mechanisms](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/hypersensitivity-reactions-types-and-mechanisms) * [Therapeutic Decision-Making for Respiratory Infections in Cattle](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/therapeutic-decision-making-respiratory-infections-cattle) * [Monitoring Fluid Therapy in Critically Ill Veterinary Patients](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/monitoring-fluid-therapy-critically-ill-veterinary) ## References and Further Reading - [Nanoparticle-Based Magnetic Resonance Imaging on Tumor-Associated Macrophages and Inflammation.](https://pubmed.ncbi.nlm.nih.gov/28588582/). 2017. - [AllergoOncology: Biomarkers and refined classification for research in the allergy and glioma nexus-A joint EAACI-EANO position paper.](https://pubmed.ncbi.nlm.nih.gov/38263898/). 2024. - [AllergoOncology: Biomarkers and Refined Classification for Research in the Allergy and Glioma Nexus - a Joint EAACI-EANO Position Paper](https://doi.org/10.22541/au.169956638.85807758/v1). 2023. - [Using the canine microbiome to bridge translation of cancer immunotherapy from pre-clinical murine models to human clinical trials.](https://pubmed.ncbi.nlm.nih.gov/36032113/). 2022. - [Davis-Thompson Foundation Veterinary Pathology Resources](https://www.davisthompsonfoundation.org/). Davis-Thompson Foundation. - [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual. - [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association. - [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). WOAH. ## Related Articles - [Monitoring Protocols for Chemotherapy in Veterinary Oncology Patients](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/monitoring-protocols-chemotherapy-veterinary-oncology) - [Monitoring Analgesic Therapy in Horses: A Practical Guide](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/monitoring-analgesic-therapy-horses-practical-guide) - [Monitoring Corticosteroid Therapy in Veterinary Dermatology](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/monitoring-corticosteroid-therapy-veterinary-dermatology) - [Fungal Pathogenesis and Host Immune Response](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/fungal-pathogenesis-and-host-immune-response) - [Monitoring Antifungal Therapy in Horses: Efficacy and Safety](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/monitoring-antifungal-therapy-horses-efficacy-safety) > This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.