Cat Cyst or Lump on the Back, Tail, or Foot

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

A cat cyst on the back is usually a benign, fluid-filled or keratin-filled pocket under the skin, but the same look can come from an abscess, an insect bite reaction, or a tumor. Location matters, because lumps on the back, tail, and foot each have their own short list of likely causes. A veterinarian can tell most of them apart with a needle sample in the exam room.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

• A soft, movable lump under the skin is often a cyst or a benign fatty growth, while a firm, fixed, fast-growing lump is more concerning for a tumor [1].
• Any lump that is hot, painful, draining, or paired with fever or limping may be an abscess or infection and needs same-day care.
• Fine needle aspiration or biopsy is how a veterinarian identifies what the lump is made of, and benign versus malignant cannot be told by feel alone [1].
• Lumps removed surgically should go to a laboratory so the type and the margins can be checked [1].
• A cyst that keeps coming back in the same spot should be rechecked, because recurrence can mean the original diagnosis was incomplete or the lesion was not fully removed [2].

What a Lump on Your Cat Actually Looks Like

Owners usually find these by petting. You may feel a pea-sized bump, a marble, or a larger soft mass. Some sit right under the skin and slide easily when you touch them. Others feel attached to deeper tissue and do not move.

Size alone does not tell you much. In a review of 220 feline dermoid cysts, the average cyst diameter was only about 1.4 cm, which is smaller than a dime [3]. A small lump can still be a tumor, and a large one can still be harmless.

Normal skin and coat vary a lot between cats. It is normal to feel the spine, the hip points, and the tail bones. It is normal to feel small, stable lumps that have been there for years and have not changed. It is not normal to find a new lump that grows over days, or one that appears with pain, heat, or discharge.

Common Causes of a Cat Cyst on the Back, Tail, or Foot

The table below groups the main possibilities by what you are likely to see and how fast you should act.

Cysts on the Back

The back is the classic spot for dermoid cysts. These are developmental abnormalities that form along the dorsal body midline, meaning the top center line of the body [3]. In cats, the neck is the most common location, reported in about 56% of cases in one large review [3]. They are lined with skin-like tissue and filled with keratin and hairs [3].

Most dermoid cysts in that review were not linked to inflammation, and about two thirds had no associated inflammatory lesions [3]. That fits the picture many owners describe, a quiet lump that never seems to bother the cat.

Dermoid cysts are not the only option. Sebaceous cysts, follicular cysts, and benign skin tumors all show up on the back. A cyst that keeps coming back after being lanced or drained often has a lining that was never removed, which is why surgery instead of drainage is often the fix.

Cysts and Lumps on the Tail

The tail is a common site for bite abscesses, because cats often get bitten there during fights. A tail lump that is painful, warm, or draining is an abscess until proven otherwise.

Tail lumps can also be cysts, benign tumors, or, less often, malignant tumors. A tumor on the tail can invade the tail tissue and may need removal of part of the tail. If your cat will not let you touch the tail, or the tail droops or drags, that is a sign of pain or nerve involvement and deserves a prompt exam.

Cysts and Lumps on the Foot

Foot lumps are often more urgent than back lumps because they affect walking. Causes include foreign bodies (foxtails, splinters, glass), abscesses, cysts, and tumors.

A cat with a foot lump may limp, lick the paw constantly, or hold the leg up. Swelling between the toes or on a pad can look like a cyst but may be an infection that needs drainage and antibiotics. If your cat is limping, see the guide on cat limping on a back leg for how to judge urgency.

When the Lump Is a Tumor

Tumors of the skin in cats can be benign or malignant [1]. Benign tumors are not invasive, do not spread, and are usually easy to remove surgically [1]. Malignant tumors can invade surrounding tissue and spread to distant organs [1].

You cannot tell the difference by looking or feeling. Distinguishing a benign tumor from a cancerous tumor requires specialized knowledge and laboratory equipment [1]. That is why a veterinarian takes a sample.

Some masses at injection sites behave aggressively. One report described a sarcoma at a previous injection site that recurred and later invaded the spinal cord, causing weakness, fecal incontinence, and urinary retention [2]. Another report described a malignant plasmacytoma at a previous vaccination site that was first misdiagnosed as lymphoma and required immunohistochemistry to identify correctly [4]. These are uncommon, but they show why a growing lump at an injection site should not be watched for months.

Red Flags That Mean Emergency or Same-Day Care

Call your veterinarian right away, or go to an emergency clinic, if you see any of these:

• A lump that is growing quickly, over hours to days
• Heat, redness, severe pain, or a cat that cries when the area is touched
• Pus, blood, or foul-smelling fluid draining from the lump
• Fever, hiding, not eating, or vomiting along with the lump
• Limping, dragging a limb, or refusing to bear weight
• A lump on the spine area with weakness, wobbling, or loss of bladder or bowel control
• Trouble breathing, especially with a lump on the chest or neck
• A lump that bleeds on its own or has an open, non-healing sore

Spinal involvement is rare but serious. A dermoid cyst compressing the spinal cord in one cat caused reduced activity and hind limb ataxia, and it was treated successfully with surgery [5]. A meningomyelocele in another cat caused progressive weakness and urinary incontinence along with a painful mass over the lower spine [6]. Neurologic signs with a back lump are an emergency.

What You Can Safely Do at Home While You Wait

Do not squeeze, poke, or try to pop the lump. You can turn a quiet cyst into an infected abscess.

Do not apply human acne creams, hydrogen peroxide, alcohol, or essential oils. Cats groom themselves, and many topical products are toxic when licked off.

What you can do:

• Take a photo of the lump next to a coin or ruler so you can track size.
• Note the date you first saw it and whether it has changed.
• Gently part the fur to check for redness, drainage, or a scab, without pressing hard.
• Check for other lumps. Run your hands over the whole body, including the tail, legs, and paw pads.
• Keep your cat indoors if the lump might be a bite abscess, so it does not get into another fight.
• Use a soft cone if your cat is licking or chewing at the lump.

If the lump is an abscess that has already opened and is draining, cover the area loosely with a clean gauze pad and get seen the same day. Do not try to flush it at home.

How Your Veterinarian Decides What the Lump Is

The exam starts with hands and history. Your vet will ask when you found the lump, whether it has changed, whether your cat goes outside, and when the last vaccines or injections were given.

Then comes sampling. A fine needle aspiration pulls a few cells with a thin needle, and a biopsy removes a small piece of tissue [1]. These samples go to a laboratory for evaluation [1]. Many cysts and fatty tumors can be identified from a needle sample alone. Others need a biopsy or full removal to get a diagnosis.

If the lump is removed, the tissue should be evaluated by a laboratory to confirm the tumor type and whether all of it was likely removed [1]. That last part is done by checking the margins, the edge of the removed tissue, under a microscope [1]. Dirty margins mean tumor cells reach the edge, so cells likely remain in the cat [1]. Narrow margins mean cells are close to the edge, so some could be left behind [1]. Wide or clean margins mean cells are far from the edge, so it is unlikely any remain [1].

Your vet may also recommend blood work, imaging, or referral to a specialist if a malignant tumor is suspected. For round cell tumors, extra testing such as immunohistochemistry may be needed to reach the right diagnosis, as one case of plasmacytoma showed after an initial misdiagnosis [4].

Treatment depends on the diagnosis. Cysts are often removed surgically, and complete removal gives the best chance of no recurrence [5]. Abscesses are drained and treated with antibiotics. Benign tumors are usually cured by surgery [1]. Malignant tumors may need wider surgery, radiation, or other treatment, and follow-up imaging is often used to watch for recurrence [2].

If you are unsure whether a lump needs a visit at all, this guide on cat skin bumps and lumps walks through when monitoring is reasonable and when it is not.

Preventing and Monitoring Lumps

You cannot prevent most cysts or tumors. Dermoid cysts are developmental, meaning the cat was born with the tissue that forms them [3]. What you can do is catch changes early.

Do a monthly lump check. Run your hands slowly from the head to the tail, down each leg, and along the tail. Feel the paw pads and between the toes. It takes two minutes.

Write down what you find. Note the location, approximate size, and how it feels (soft, firm, movable, fixed). Compare month to month.

Pay extra attention to injection sites. If a lump appears where your cat was vaccinated or given an injection, tell your vet the date of that injection. Recurrent masses at injection sites have been reported to behave aggressively [2][4].

Keep up with routine exams. Your vet can feel lumps you might miss, especially on the belly, behind the legs, and under the chin.

If your cat has a cyst that keeps coming back, ask about surgical removal instead of another drainage. Recurrence often means the cyst lining is still there.

Limitations and When to Contact a Veterinarian

This article cannot tell you what your cat's lump is. Only an exam and often a lab sample can do that.

Contact your veterinarian the same day if a lump is new and painful, warm, draining, or growing, or if your cat is limping, off food, or hiding.

Go to an emergency clinic now if your cat has trouble breathing, cannot walk, has lost bladder or bowel control, has a lump that will not stop bleeding, or has a rapidly swelling area around the face or throat.

Schedule a routine visit within a week or two if you find a small, soft, movable lump that is not bothering your cat, especially if it has been there a while without change.

Every cat is different, and your veterinarian needs to see your cat to make a plan.

Frequently Asked Questions

Is a cyst on my cat's back dangerous?

Most cysts are benign and not dangerous, but you cannot confirm that by feel. A veterinarian needs a needle sample or biopsy to tell a cyst from a tumor [1]. If the lump is soft, movable, and unchanged for months, the risk is lower, but it still deserves a look.

Why does my cat's cyst keep coming back?

Recurrence usually means the cyst lining was not fully removed. Drainage or lancing removes the contents but leaves the wall, so fluid refills. Surgical removal of the whole cyst gives the best chance of a cure [5]. A lump that regrows after surgery should be rechecked, because recurrence can also happen with more aggressive masses [2].

Can I pop a cyst on my cat at home?

No. Popping or squeezing can push bacteria deeper and turn a harmless cyst into an abscess. It also causes pain and can make your cat defensive. Leave it alone and let your veterinarian decide whether it needs drainage or removal.

Does a lump on the tail mean cancer?

Usually not, but it can. Tail lumps are often bite abscesses or cysts. Malignant tumors can also form on the tail and may invade local tissue [1]. Because the tail is easy to examine, a vet can often sample it quickly in the office.

How long can I watch a lump before seeing a vet?

If the lump is small, soft, movable, and not changing, a routine visit within a couple of weeks is reasonable. If it grows, becomes painful, drains, or your cat starts limping or acting sick, do not wait. Fast-growing or injection-site lumps should be seen promptly [2][4].

Related Articles

• Cat Hair Loss on Back Near Tail: What It Means
• Cat Limping on a Back Leg: Causes and Urgency Guide
• Cat Skin Bumps and Lumps: When to See a Vet and When to Monitor
• Cat Skin Rash on Back: Causes and Treatment
• Ear Polyps in Cats: Signs, Diagnosis, Surgery, and Recurrence
• Abdominal Ultrasound in Cats: Normal Findings and Common Abnormalities
• Lumps on a Cat's Back, Neck, or Tail: What They Mean
• Lump on Your Cat's Leg or Foot: What It Could Be
• Cysts in Cats: Skin, Belly, Kidney, and Leg Lumps

References

1. Tumors of the Skin in Cats - Cat Owners. Merck Veterinary Manual.
2. Suspected recurrent sarcoma resembling feline injection-site sarcoma with spinal cord invasion in a cat. JFMS open reports, 2026.
3. Feline dermoid cyst: Retrospective case series and literature review. Veterinary pathology, 2025.
4. A Rare Case of Malignant Plasmacytoma at a Previous Injection Site in a Cat. Veterinary sciences, 2026.
5. A feline spinal dermoid cyst treated with surgical intervention. The Journal of veterinary medical science, 2024.
6. Case Report: Surgical management of a meningomyelocele in a cat. Frontiers in veterinary science, 2026.

Further Reading

• Dermatitis and Dermatologic Problems in Cats - Cat Owners (Merck Veterinary Manual)
• Merck Veterinary Manual: Cat Owners
• Cornell Feline Health Center: Health Information