# Surgical Oncology: Biopsy Techniques and Margin Assessment


## Key Takeaways

- Biopsy technique selection hinges on tumor characteristics: incisional biopsy is preferred for large, deeply invasive, or high-grade tumors, or when neoadjuvant therapy is planned, while excisional biopsy is suitable for small, superficial, well-circumscribed masses where complete removal is feasible.
- Accurate margin assessment is critical for oncologic outcomes and requires meticulous surgical technique, including pre-fixation inking of surgical borders with distinct colors and precise orientation of the specimen for the pathologist.
- Histologic grading, particularly for soft tissue sarcomas, is essential for predicting biologic behavior and guiding therapeutic decisions, with parameters like mitotic index and vascular invasion being key components.
- Sentinel lymph node biopsy is a vital staging procedure, feasible even after prior local excision, and crucial for accurate nodal staging as the sentinel node often differs from the anatomically expected regional node.
- Specimen handling and submission are paramount; gentle handling, immediate and adequate formalin fixation (minimum 10:1 ratio), clear labeling, and detailed submission forms with diagrams are mandatory for meaningful margin evaluation and diagnosis.
- Intraoperative margin assessment techniques, such as multimodal nonlinear optical imaging, are emerging but currently, reliance remains on meticulous postoperative histopathologic evaluation, emphasizing the collaborative role of the surgeon and pathologist.

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This article provides a practical framework for selecting and performing biopsy techniques in dogs and cats with suspected neoplasia, and for assessing surgical margins for completeness. It serves the practicing veterinarian who must decide between cytology, incisional biopsy, and excisional biopsy, and who must interpret the pathology report that follows. The clinical questions addressed are direct: which technique for which tumor, how to sample without compromising definitive surgery, and how to determine whether a resection is complete.

The pathology report is the single most influential document in oncologic case management. It determines prognosis, guides therapeutic decisions, and shapes overall case strategy, which means diagnostic accuracy, completeness, and clarity are non-negotiable. Successful management depends on collaboration between the clinician, the oncologist, and the pathologist, and that collaboration begins with the quality of the specimen submitted. Consensus guidelines from the American College of Veterinary Pathologists Oncology Committee provide a standardized approach to submission, trimming, margin evaluation, and reporting of neoplastic biopsy specimens, and these guidelines form the backbone of the recommendations that follow.

## At a Glance

| Parameter | Decision or Fact |
|---|---|
| Biopsy method selection | Based on tumor size, location, suspected biologic behavior, and impact on definitive surgery |
| Incisional biopsy | Preferred for large tumors, suspected high-grade malignancies, or when neoadjuvant therapy is planned |
| Excisional biopsy | Appropriate for small, superficial, well-circumscribed tumors when complete excision is achievable |
| Margin assessment | Requires ink applied to surgical borders before formalin fixation, with margins reported as complete, close, or incomplete |
| Histologic grading | Soft tissue sarcomas should be graded using a published system to predict biologic behavior |
| Sentinel lymph node biopsy | Feasible even after prior local excision, and the sentinel node often differs from the regional node |
| Specimen handling | Orientation sutures, margin inks, and a detailed submission form are mandatory for meaningful margin evaluation |

## Biopsy Technique Selection

The choice of biopsy technique is a surgical decision with therapeutic consequences. Cytology should precede biopsy in most cases because it is rapid, inexpensive, and may confirm neoplasia. However, cytology cannot provide architectural information, stromal invasion patterns, or accurate histologic grading, and it cannot distinguish some reactive from neoplastic processes. When cytology is non-diagnostic or when treatment decisions require histologic detail, biopsy is indicated.

Incisional biopsy is the technique of choice for tumors that are large, deeply invasive, or located where wide excision would be disfiguring or functionally compromising. It provides a tissue diagnosis before definitive surgery, allowing the surgeon to plan resection margins, staging tests, and adjunctive therapy. For canine cutaneous and subcutaneous soft tissue sarcomas, cytology and biopsy are important for presurgical planning, and wide surgical excision with margins greater than 3 cm decreases the likelihood of tumor recurrence. Incisional biopsy is also indicated when neoadjuvant chemotherapy or radiation therapy is contemplated, because the histologic diagnosis and grade will determine whether such therapy is appropriate.

Excisional biopsy is appropriate when the entire tumor can be removed with adequate margins in a single procedure. This applies to small, superficial, well-circumscribed masses where the cosmetic and functional cost of wide excision is acceptable. Excisional biopsy is also reasonable when the index of suspicion for malignancy is low and the mass is small enough that complete removal is straightforward. The disadvantage is that if margins are incomplete, the surgical bed may be contaminated, and the subsequent wide re-excision must encompass the entire previous surgical field.

## Incisional Biopsy Technique

Incisional biopsy requires a scalpel blade, not a biopsy punch, for most soft tissue sarcomas and other infiltrative tumors. The incision should be oriented along the long axis of the limb or parallel to skin tension lines so that the biopsy tract can be excised en bloc with the definitive resection. A wedge or elliptical sample that includes the tumor periphery and adjacent normal tissue is preferred, because the interface between neoplastic and normal tissue provides the pathologist with the most diagnostic information.

The biopsy incision must be placed so that it does not compromise subsequent surgery. This means avoiding dissection into tissue planes that will be needed for closure, avoiding major neurovascular structures, and ensuring that the biopsy tract lies within the field of the planned wide excision. Hemostasis should be meticulous, and the biopsy site should be closed in layers to minimize hematoma formation. A single dose of perioperative antibiotics is reasonable, but prolonged antimicrobial therapy is not indicated for routine biopsy.

Needle biopsy techniques, including core needle biopsy, have a role in specific circumstances. They are less invasive, can be performed with ultrasound guidance, and are useful for deep masses where surgical biopsy would require substantial dissection. The limitation is sample size: core biopsies may not capture the most representative portion of a heterogeneous tumor, and they may not provide enough tissue for grading. The American College of Veterinary Pathologists guidelines emphasize that the diagnostic yield depends on the number and size of cores and on the experience of the operator.

## Excisional Biopsy and Resection Principles

Excisional biopsy is a therapeutic procedure that also serves a diagnostic purpose. The surgeon must remove the entire tumor with a cuff of normal tissue, and the width of that cuff depends on the suspected tumor type and grade. For soft tissue sarcomas, wide margins greater than 3 cm are associated with lower recurrence rates, although the minimum acceptable margin width remains an area of ongoing investigation. For mast cell tumors, the recommended margin varies with histologic grade, and the surgeon should have a working knowledge of the current grading schemes before planning resection.

The specimen must be oriented for the pathologist. This is accomplished with sutures placed at specific locations, a diagram in the submission form, or both. A common convention is a single suture at the proximal or cranial margin and two sutures at a second designated margin. The surgeon should ink the margins before fixation, using different colors for different surgical borders, because formalin penetrates tissue slowly and ink applied after fixation will not penetrate adequately. The pathology laboratory can also ink margins, but the surgeon's orientation and inking at the time of surgery is more reliable.

## Margin Assessment and Reporting

Margin assessment begins in the operating room and continues in the pathology laboratory. The pathologist must know which surfaces are true surgical margins and which are artifacts of dissection. The American College of Veterinary Pathologists consensus guidelines recommend that margins be reported as complete, close, or incomplete, with the distance from the neoplastic cells to the inked margin measured in millimeters. A close margin is one where neoplastic cells approach but do not reach the ink, and the threshold for "close" varies by tumor type and grade.

The clinical significance of a close margin depends on the tumor's biologic behavior. A low-grade soft tissue sarcoma with a 1 mm margin may behave differently from a high-grade sarcoma with the same margin, and the histologic grading scale is useful in predicting biologic behavior. The pathologist's report should include the histologic type, grade, mitotic index, presence or absence of vascular invasion, and the margin status, and the clinician must interpret these findings in the context of the individual patient.

## Intraoperative Assessment and Emerging Techniques

Traditional margin assessment is postoperative, which means an incomplete resection requires a second surgery. Intraoperative techniques that provide real-time information about margins are an active area of investigation. Label-free multimodal nonlinear optical imaging has been adapted into portable systems for intraoperative assessment of resected tissue, and this technology can visualize microstructural features and molecular dynamics without exogenous contrast agents. The diagnostic feasibility of imaging core needle biopsy specimens during veterinary cancer surgeries has been demonstrated, suggesting that real-time margin assessment may become clinically available.

Sentinel lymph node biopsy is a related staging procedure that has gained acceptance in veterinary oncology. It is feasible in dogs with scars from prior local excision of solid malignancies, with a detection rate of 91.2 percent in one series, and the sentinel node did not correspond to the regional lymph node in 61.3 percent of cases. This finding has direct clinical relevance: staging based on the regional node alone will misclassify a substantial proportion of patients. Sentinel lymph node biopsy should be considered for accurate nodal staging, particularly for mast cell tumors, even when the primary tumor has already been excised.

## Biopsy Handling and Specimen Submission

The diagnostic value of a biopsy depends as much on post-acquisition handling as on the surgical technique itself. Tissue removed for histopathology should be handled gently with forceps on the margin or edge only, never crushed with thumb forceps on the diagnostic face. Specimens should be placed immediately in fixative at a volume of at least 10 parts formalin to 1 part tissue. Large specimens should be sectioned to permit penetration, but the cut surfaces must be identified for the pathologist with suture or ink so that orientation is preserved.

The [American College of Veterinary Pathologists Oncology Committee guidelines for tumor biopsy submission](https://pubmed.ncbi.nlm.nih.gov/21123864/) recommend that each specimen be submitted in a separate, clearly labelled container with the anatomical site, the orientation of the specimen, and the surgical findings recorded. A diagram or photograph of the lesion with margin locations marked is more useful than a written description alone. For multiple biopsies from the same patient, each site should be labelled separately instead of pooled, because the pathologist cannot assign histologic grade or margin status to a specific location from a pooled sample.

Incisional biopsy samples should be taken from the viable, non-necrotic periphery of the lesion. Central necrosis and inflammation obscure the diagnostic architecture and may lead to a non-diagnostic report. If the lesion is heterogeneous, sample multiple regions and submit them separately. For lesions where the clinical suspicion is high-grade sarcoma or round cell tumor, the biopsy tract should be planned so that it can be excised en bloc with the definitive resection. The tract itself is a potential route of tumor dissemination and must be considered part of the surgical field at the time of curative resection.

## Margin Inking and Orientation

Margin assessment begins in the operating room, not the pathology laboratory. The surgeon is responsible for orienting the specimen so that the pathologist can report margin status accurately. The [ACVS guidance on surgical oncology case management](https://www.acvs.org/small-animal/) emphasizes that the surgeon should ink the margins before fixation using a color-coded system, typically with the deep margin in one color and the peripheral margins in another. A written key must accompany the specimen.

The recommended approach is to paint the entire cut surface of the specimen with India ink or commercial tissue dye, allow it to dry, and then place the specimen in formalin. The pathologist will section perpendicular to the inked surfaces. If the specimen is not inked, the pathologist can only report margins as unassessable, which forces a clinical decision based on incomplete information. The [veterinary pathology consensus guidelines](https://pubmed.ncbi.nlm.nih.gov/21123864/) note that margin evaluation is only as reliable as the orientation provided by the submitting clinician.

For excisional biopsies of small lesions, the entire specimen should be submitted. For larger resections, the surgeon should mark the closest gross margin with a suture and note this on the submission form. The pathologist can then focus sectioning on the area of greatest concern instead of sampling the specimen at random.

## Margin Assessment Protocol

A standardized margin assessment protocol improves the consistency of histopathologic reporting and the clinical decisions that follow. The following protocol is adapted from the [ACVP Oncology Committee recommendations](https://pubmed.ncbi.nlm.nih.gov/21123864/) and is suitable for routine small animal practice.

| Step | Action | Purpose |
|------|--------|---------|
| 1 | Record gross dimensions and lesion location before fixation | Provides baseline for margin measurement |
| 2 | Ink margins with color-coded dyes, record the key | Allows pathologist to identify specific margins |
| 3 | Section specimen perpendicular to inked margins | Enables measurement of distance from tumor to ink |
| 4 | Submit all margins or the closest margin with a map | Ensures the critical margin is evaluated |
| 5 | Report margin distance in millimetres for each inked surface | Provides quantitative data for recurrence risk |
| 6 | Record histologic grade and mitotic count | Combines with margin status for prognostic assessment |

The margin distance reported by the pathologist is the distance from the tumor edge to the inked surgical surface. A margin is considered complete when no tumor cells are present at the inked edge, regardless of the measured distance. However, the clinical significance of a narrow but complete margin depends on tumor biology. For canine soft tissue sarcoma, [evidence-based case management recommendations](https://pubmed.ncbi.nlm.nih.gov/26808432/) note that wide surgical excision with margins greater than 3 cm decreases the likelihood of recurrence, but the minimum acceptable margin width remains undefined and is likely tumor-grade dependent.

## Species and Anatomic Site Considerations

The correct biopsy technique and margin approach vary with species, tumor type, and anatomic location. In cats, injection-site sarcomas require a different surgical strategy than cutaneous mast cell tumors. The biopsy tract must be planned to allow wide excision of the tract with the tumor, and the deep margin is often the limiting factor because of the difficulty of achieving wide margins over the dorsal thorax or between the scapulae. Preoperative imaging, including computed tomography, is frequently required to plan the resection and to assess the deep margin.

In dogs, the approach to a subcutaneous mass depends on the cytologic diagnosis. A well-differentiated lipoma can be managed with marginal excision, whereas a soft tissue sarcoma requires wide excision with the biopsy tract included. The [MSD Veterinary Manual guidance on tumor staging and biopsy](https://www.msdvetmanual.com/) advises that cytology should precede biopsy in most cases, because it is rapid, inexpensive, and may change the biopsy technique selected. A cytologic diagnosis of mast cell tumor, for example, should prompt lymph node assessment and a wider surgical plan than a cytologic diagnosis of lipoma.

Oral tumors present a specific challenge. The [porcine pseudotumor model for oral cancer biopsy training](https://pubmed.ncbi.nlm.nih.gov/38500112/) highlights that surgeons do not always maintain a safe margin during oral tumor resection, and the same study identifies biopsy difficulty as a recognized problem in clinical practice. In the oral cavity, incisional biopsy is preferred for lesions larger than 2 cm or where the resection would be disfiguring. The biopsy should be taken from the advancing edge of the lesion, including a small amount of adjacent normal tissue, and the depth should extend into the underlying submucosa or bone where indicated.

## Sentinel Lymph Node Assessment

Sentinel lymph node biopsy has become a standard staging tool in canine oncology, and it is feasible even in patients with scars from prior local excision. A [study of sentinel lymph node biopsy in dogs with prior excision scars](https://pubmed.ncbi.nlm.nih.gov/36077914/) demonstrated a detection rate of 91.2% using lymphoscintigraphy, methylene blue, or near-infrared fluorescence imaging, with the sentinel node differing from the expected regional lymph node in 61.3% of cases. This finding has direct clinical relevance: relying on the anatomically expected lymph node will misidentify the true draining node in a substantial proportion of patients.

The timing of sentinel lymph node biopsy relative to the primary tumor excision is flexible. The same study found that the procedure was successful at a median of 50 days after the original excision, which permits staging in patients referred after incomplete resection. Sentinel lymph node biopsy should be considered in any patient with a histologically confirmed malignancy where nodal status would change the treatment plan, particularly mast cell tumors, oral melanomas, and high-grade soft tissue sarcomas.

## Intraoperative Imaging and Emerging Techniques

Real-time intraoperative assessment of margins remains an area of active development. [Label-free multimodal nonlinear optical imaging](https://pubmed.ncbi.nlm.nih.gov/33746497/) has been adapted into a portable system that can image core needle biopsy specimens during veterinary cancer surgeries. This technique provides information about the tumor microenvironment and margin status without the need for exogenous contrast agents, which can perturb the natural tissue architecture. The technology is not yet widely available in clinical practice, but it represents a direction of travel toward point-of-procedure margin assessment that may reduce the need for repeat surgery.

For the practising veterinarian, the practical implication is that margin assessment remains a histopathologic exercise. The surgeon should plan the resection as though the margins will be evaluated, submit the specimen with complete orientation data, and use the pathology report to guide the need for re-excision or adjuvant therapy. The [ACVS small animal resources](https://www.acvs.org/small-animal/) reinforce that the surgeon and pathologist function as a team, and the quality of the pathology report is directly proportional to the quality of the specimen submitted.

## Complications and Failure Modes

Biopsy procedures fail in predictable patterns. The most consequential failure is sampling error, where the biopsy specimen does not represent the lesion. This occurs when the sample is taken from necrotic, inflamed, or reactive tissue adjacent to viable neoplastic cells. Discriminating features include a specimen that is soft, friable, or discolored, or a histologic report describing only inflammation, necrosis, or granulation tissue when the clinical appearance suggests neoplasia. Repeat sampling from the periphery of the lesion, where viable cells are more likely to reside, is the corrective action.

Hemorrhage is the most common intraoperative complication. It is usually self-limiting with direct pressure, but arterial hemorrhage from a deep incisional biopsy may require ligation or vessel sealing. Postoperative hematoma formation can obscure residual tumor and complicate subsequent margin assessment. Seroma formation is more common after large excisional biopsies and can delay wound healing or become infected.

Wound dehiscence and surgical site infection occur more frequently when biopsy tracts are placed in poorly vascularized tissue, when tension is placed on closure, or when the biopsy site is contaminated. The biopsy tract itself must be considered contaminated with neoplastic cells and should be excised en bloc with the tumor at the time of definitive resection. Failure to do so leaves a tract of neoplastic cells that can seed the surgical wound.

Tumor seeding along the biopsy tract is a recognized but uncommon complication. Fine-needle aspiration carries the lowest risk, while large-bore needle biopsies and incisional biopsies carry higher risk. The risk is minimized by placing the biopsy incision directly over the tumor in a location that will be incorporated into the definitive resection field.

| Observation | Likely cause | Discriminating check |
|---|---|---|
| Histology reports necrosis or inflammation only | Sampling error from nonrepresentative tissue | Repeat biopsy from lesion periphery, compare with cytology |
| Persistent hemorrhage after biopsy | Arterial laceration or coagulopathy | Direct pressure, ligation, check platelet count and coagulation profile |
| Delayed wound healing or discharge | Infection, tension, or devitalized tissue | Culture, reassess closure tension, evaluate tissue perfusion |
| Recurrence at biopsy site | Tumor seeding along tract | Excise entire tract at definitive resection, review original biopsy location |

## Common Errors and Corrective Actions

The most frequent error in biopsy technique is selecting an incision that cannot be incorporated into the definitive resection. A transverse incision over a limb mass, for example, may force a wider resection than a longitudinal incision would have required. The corrective action is to plan the biopsy incision parallel to the long axis of the limb and within the boundaries of the anticipated resection.

Inadequate sample size is another recurring error. A 2 mm punch biopsy of a large, heterogeneous mass may capture only the necrotic center. The corrective action is to obtain multiple samples from different regions of the mass, including the interface between tumor and normal tissue. For masses larger than 5 cm, at least three separate samples are recommended.

Crush artifact from forceps or hemostats renders tissue uninterpretable. The corrective action is to handle tissue gently with fine forceps or skin hooks and to avoid crushing the specimen at any point. Electrocautery should not be used to excise the biopsy specimen itself, as thermal artifact destroys cellular detail. Cautery may be used for hemostasis after the specimen is removed.

Submitting specimens without orientation is a common error that prevents margin assessment. The corrective action is to place orientation sutures or ink before specimen removal and to document the orientation on a diagram or photograph. The [recommended guidelines for submission, trimming, margin evaluation, and reporting of tumor biopsy specimens in veterinary surgical pathology](https://pubmed.ncbi.nlm.nih.gov/21123864/) provide a standardized framework for this process.

## Limitations of Current Evidence

The evidence base for many biopsy and margin decisions in veterinary oncology rests on expert consensus instead of controlled trials. The American College of Veterinary Pathologists Oncology Committee guidelines acknowledge that many recommendations represent collective experience and have not met the rigors of definitive scientific study. This is particularly true for optimal margin width, where the minimum surgical margin for soft tissue sarcoma remains undetermined, as noted in the [evidence-based review of canine soft tissue sarcoma case management](https://pubmed.ncbi.nlm.nih.gov/26808432/).

Expert opinion differs on several points. The clinical significance of a narrow but clean margin, defined as tumor cells within 1 to 2 mm of the inked edge, remains contested. Some pathologists report these as complete excisions, while others recommend adjuvant therapy. The biologic behavior of the tumor, its grade, and its anatomic location should inform the interpretation of margin status more than the absolute measurement alone.

Intraoperative margin assessment remains an area of active development. Label-free multimodal nonlinear optical imaging has shown diagnostic feasibility for assessing core needle biopsy specimens during veterinary cancer surgeries, but this technology is not yet widely available in clinical practice. Until such tools are validated and disseminated, the surgeon must rely on careful gross inspection, palpation, and histologic margin assessment.

## Referral and Escalation Criteria

Referral to a surgical or medical oncologist is warranted when the tumor is large, recurrent, or located in an anatomically complex region where wide resection would compromise function. Tumors with known high metastatic potential, such as high-grade mast cell tumors, hemangiosarcoma, and osteosarcoma, benefit from staging and multidisciplinary planning before surgery.

Pathologist consultation is appropriate when the histologic diagnosis does not match the clinical behavior, when margin status is ambiguous, or when the tumor grade will materially change the treatment recommendation. Many diagnostic laboratories offer slide review by a second pathologist or a specialist in oncologic pathology.

Regulatory reporting obligations vary by jurisdiction. The [WOAH terrestrial animal health code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) addresses reportable diseases that may present as mass lesions, and the [AVMA practice resources](https://www.avma.org/resources-tools) provide guidance on professional obligations. Clinicians should be familiar with the reporting requirements in their region and should contact their local veterinary authority when a mass lesion is suspected to be a notifiable disease.

## Frequently Asked Questions

### How Should I Prioritize Biopsy Method When Cost or Equipment Is Limited?

When advanced imaging or specialized biopsy instruments are unavailable, a standard surgical blade and careful technique remain reliable. Incisional wedge biopsy with a No. 11 or No. 15 blade provides diagnostic tissue for most superficial masses. For deeper lesions, a Tru-Cut needle or punch biopsy often suffices. Prioritize obtaining tissue from the viable, non-necrotic periphery of the mass instead of the center. Submit multiple samples when feasible. The [ACVS small animal resources](https://www.acvs.org/small-animal/) describe standard surgical approaches that do not require specialized equipment. If only cytology is affordable initially, proceed with fine-needle aspiration, but recognize that architectural information and accurate grading require histopathology. Communicate clearly to the owner which diagnostic limitations exist with each option.

### What Should I Do When Histopathology Reports an Incomplete Margin?

An incomplete margin does not mandate immediate re-excision in every case. Assess the tumor type, histologic grade, anatomic location, and the width of the incomplete area. For low-grade soft tissue sarcomas, the [evidence-based review of canine soft tissue sarcoma management](https://pubmed.ncbi.nlm.nih.gov/26808432/) notes that wide excision decreases recurrence, but observation may be reasonable for select low-grade tumors where re-excision carries substantial morbidity. Discuss options with the owner: re-excision, radiation therapy, or monitoring. If re-excision is chosen, the scar and previous biopsy tract must be excised en bloc with the new margins. Submit the entire specimen with orientation sutures and a diagram. If the pathologist reported tumor cells at the inked margin, the biologic significance depends on tumor grade and inherent metastatic potential.

### How Do I Orient and Ink a Specimen When the Laboratory Does Not Provide a Kit?

Standard surgical ink or tissue dyes are inexpensive and widely available. India ink, tattoo ink, or commercial tissue dyes applied with a cotton-tipped applicator work reliably. Dry the specimen surface gently with gauze before applying ink to prevent smearing. Use different colors for distinct margins, or apply one color and document the orientation with suture tags and a written diagram. The [ACVP Oncology Committee biopsy submission guidelines](https://pubmed.ncbi.nlm.nih.gov/21123864/) emphasize that clear communication between surgeon and pathologist is essential for accurate margin evaluation. If no ink is available, place sutures at specific clock positions and describe them in the submission form. Photograph the specimen before fixation. Never place the specimen in formalin before inking, as fixation alters tissue consistency and ink adherence.

### Can Sentinel Lymph Node Biopsy Be Performed After a Prior Excision?

Yes. Sentinel lymph node mapping is feasible in dogs with scars from prior tumor excision, with a reported detection rate of 91.2% in one study of 34 scars. The sentinel node did not correspond to the regional lymph node in 61.3% of cases, which underscores the importance of mapping instead of blind extirpation of the nearest node. The [sentinel lymph node biopsy feasibility study](https://pubmed.ncbi.nlm.nih.gov/36077914/) demonstrated that lymphoscintigraphy, methylene blue, and near-infrared fluorescence all remain effective after previous surgery. This is clinically relevant when a marginal excision was performed without nodal staging and the owner now seeks complete staging. Perform mapping before re-excision whenever possible, as the second surgery can alter lymphatic drainage patterns.

### How Should I Document Biopsy and Margin Information in the Medical Record?

Record the lesion location, size, gross appearance, and relationship to surrounding structures before any tissue is removed. Document the biopsy technique used, the number of samples, and the orientation system applied. Include a diagram or photograph showing margin colors, suture positions, and the biopsy tract. The [ACVP Oncology Committee guidelines](https://pubmed.ncbi.nlm.nih.gov/21123864/) recommend that the submission form state the clinical suspicion, prior cytology results, and specific questions for the pathologist. Record the exact location of any incompletely excised area in the surgical report so that re-excision or radiation planning can target the correct site. Note the method of hemostasis and whether drains were placed, as these affect postoperative interpretation of imaging and clinical signs.

### How Do I Explain an Incomplete Margin to the Owner Without Causing Panic?

Use clear, non-technical language while remaining accurate. Explain that the pathologist found tumor cells extending to the edge of the removed tissue, which means microscopic disease may remain. Emphasize that this finding does not always lead to recurrence, and that options exist. The [MSD Veterinary Manual professional resources](https://www.msdvetmanual.com/) provide background on tumor behavior that can help frame the discussion. Present the treatment options in order of recommendation: re-excision, radiation therapy, or monitoring. Provide the expected outcomes for each option based on tumor type and grade. Avoid absolute statements about cure or recurrence. Offer to arrange a consultation with an oncologist or surgeon if the owner wishes. Document the discussion in the medical record, including the owner's decision and the rationale.

## Related Clinical & Scientific Guides

* [Perioperative Antibiotic Prophylaxis: Timing and Selection](/knowledge/veterinary-medicine/veterinary-surgery/perioperative-antibiotic-prophylaxis-timing-selection)
* [Surgical Approaches to the Femur and Stifle](/knowledge/veterinary-medicine/veterinary-surgery/surgical-approaches-femur-stifle)
* [Fracture Healing Assessment: Radiographic and Clinical Evaluation](/knowledge/veterinary-medicine/veterinary-surgery/fracture-healing-assessment-radiographic-clinical)


## References and Further Reading

- [Intraoperative Label-Free Multimodal Nonlinear Optical Imaging for Point-of-Procedure Cancer Diagnostics.](https://pubmed.ncbi.nlm.nih.gov/33746497/). 2021.
- [Recommended guidelines for submission, trimming, margin evaluation, and reporting of tumor biopsy specimens in veterinary surgical pathology.](https://pubmed.ncbi.nlm.nih.gov/21123864/). 2011.
- [Canine Cutaneous and Subcutaneous Soft Tissue Sarcoma: An Evidence-Based Review of Case Management.](https://pubmed.ncbi.nlm.nih.gov/26808432/). 2016.
- [Modern criteria to establish human cancer etiology.](https://pubmed.ncbi.nlm.nih.gov/15289363/). 2004.
- [Sentinel Lymph Node Biopsy Is Feasible in Dogs with Scars from Prior Local Excision of Solid Malignancies.](https://pubmed.ncbi.nlm.nih.gov/36077914/). 2022.
- [Development and validation of a cadaveric porcine Pseudotumor model for Oral Cancer biopsy and resection training.](https://pubmed.ncbi.nlm.nih.gov/38500112/). 2024.
- [American College of Veterinary Surgeons Animal Health Resources](https://www.acvs.org/small-animal/). American College of Veterinary Surgeons.
- [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.

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> 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.