Bump on a Cat's Anus: Lumps, Tumors, and What They Mean

Name: Bump on a Cat's Anus: Lumps, Tumors, and What They Mean
Creator: Dr. Zubair Khalid

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

A cat bump on anus is most often an anal sac problem, such as an impaction or an abscess, but it can also be a benign polyp or a malignant tumor. The only way to know which one you are dealing with is a veterinary exam, because the lumps can look and feel similar from the outside. This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

Anal sac disease is much less common in cats than in dogs, and the most common form in cats is impaction, where the sac clogs instead of draining [1].
An abscess usually shows up as an oozing sore next to the anus, while an impacted gland feels like a hard mass in the sac area [1].
Tumors of the anal sac do happen in cats and can be malignant, including anal sac gland carcinoma and squamous cell carcinoma [2][3].
Any lump that is growing, bleeding, ulcerated, or paired with straining, scooting, or pain needs a veterinary visit, not home treatment.
Never squeeze, lance, or apply human ointments to a lump near the anus. You can cause bleeding, infection, or a delay in diagnosis.

What You Are Seeing and What Is Normal

The anus sits at the end of the rectum, and on each side of it are two small anal sacs. These glands are the feline version of a skunk's scent glands. They make a small amount of dark, foul-smelling liquid that normally gets squeezed out when your cat poops [1].

A normal cat rear end is smooth and symmetrical. You should not feel firm knots, see open sores, or notice swelling on one side. Some cats have a small amount of dark material right at the opening, and that is usually just gland secretion.

What owners describe as a "bump" can be several different things. It may be a swollen gland under the skin, a raised red sore, a white or pale nodule, or a dark patch that looks like a blood blister. Location matters too. A lump right at the rim of the anus is different from one an inch away on the tail base or perineum.

Causes of a Cat Lump on the Anus

Anal Sac Impaction

This is the most common anal sac problem in cats [1]. The sac fills with thick, dark secretion and cannot empty. You may feel a hard mass in the area of the sac, and your cat may scoot, lick the rear end, or strain to poop [1].

Anal Sac Infection and Abscess

If bacteria get into a blocked sac, it can become infected and then abscessed. An abscess often drains on its own, leaving an oozing sore next to the anus [1]. These are painful. Your cat may cry when pooping, sit awkwardly, or refuse to be picked up.

Polyps and Adenomas

Benign growths such as rectal polyps and adenomas can protrude near the anus. For rectal polyps and adenomas, removal through the anus or with an endoscope is often curative [4]. These tend to be slow growing and may cause bleeding or straining instead of severe pain.

Malignant Tumors

Cancer of the anal sac does occur in cats. One report described a firm, painful swelling in the perianal region of a 15-year-old cat that turned out to be anal sac gland carcinoma, a tumor that invaded the surrounding muscle [2]. A separate report described two cats with squamous cell carcinoma of the anal sac, a cancer that should be on the list of possible diagnoses whenever an anal sac mass is found [3].

These tumors can spread. One cat with apocrine gland anal sac adenocarcinoma had cancer that reached lymph nodes, peripheral nerves, and the cauda equina, the bundle of nerves at the end of the spinal cord [5]. Another cat with the same tumor type had spread to regional lymph nodes and lungs [6].

Other Lumps That Can Appear in This Area

Not every perianal mass is a gland tumor. In dogs, the perianal area can also develop mast cell tumors, lymphoma, melanoma, and rarely hemangiosarcoma [7]. Cats can develop similar oddities, which is why a sample of the tissue matters more than the way the lump looks.

Cause	Typical clues	How urgent
Anal sac impaction	Hard mass in the sac area, scooting, straining to poop, licking the rear end [1]	See your vet within a few days
Anal sac abscess	Oozing sore next to the anus, swelling, pain when sitting or pooping [1]	Same day, sooner if your cat seems very painful
Rectal polyp or adenoma	Slow-growing lump, sometimes bleeding, often found on a routine exam [4]	Routine visit, then removal is often curative [4]
Anal sac carcinoma	Firm, painful perianal swelling, may invade muscle, can spread to lymph nodes and nerves [2][5]	Prompt visit, within days, not weeks
Squamous cell carcinoma of the anal sac	Anal sac mass that does not behave like a simple impaction [3]	Prompt visit, within days
Dark or blood-filled lump	Dark bump on cat anus that looks like a blood blister or bruise	Same day, because bleeding tumors need fast assessment

Red Flags That Make It an Emergency

Call an emergency clinic right away if you see any of these.

Heavy bleeding from the area that does not stop with gentle pressure.
A lump that has ruptured and is draining pus or foul fluid along with a fever, lethargy, or refusal to eat.
Sudden inability to poop at all, with repeated unproductive straining.
Severe pain, such as crying out when sitting or touching the rear end.
A rapidly growing mass, or one that has doubled in size over a few days.
Weakness in the back legs, loss of tail tone, or loss of bladder control. These can signal tumor spread to nerves, which has been reported with anal sac adenocarcinoma in a cat [5].

Safe Things You Can Do at Home While You Wait

You cannot diagnose or treat this at home, but you can keep your cat comfortable and avoid making things worse.

Do not squeeze, poke, or try to pop the lump. You can rupture a tumor or push infection deeper.
Do not apply human creams, antibiotic ointments, or essential oils. Cats groom these areas and will swallow whatever you put there.
Keep the area clean and dry. A warm damp cloth held gently against the outside for a minute or two can soothe irritation, but stop if your cat resists.
Use a cone if your cat is licking or biting the area raw.
Note the size, color, and texture of the lump, plus when you first saw it. Take a photo with a ruler or coin next to it for scale. This helps your vet track change over time.
Watch the litter box. Note straining, blood, small stool size, or accidents outside the box.
Keep your cat indoors so you can monitor eating, drinking, and bathroom habits.

If the lump is on the skin near the tail base instead of the anus itself, our guide to Cat Skin Bumps and Lumps: When to See a Vet and When to Monitor covers how to track those at home. If you are also seeing redness and irritation around the rear end or elsewhere, Cat Skin Rash with Bumps: Common Causes and Next Steps explains what different patterns usually mean.

What the Veterinarian Will Check and Test

The Physical Exam

A rectal examination is usually done to diagnose anal sac disease [1]. Your vet will insert a gloved finger to feel the sacs, the rectal wall, and the tissue around the anus. They are checking for symmetry, firmness, whether the mass is fixed to deeper tissue, and whether the sacs can be expressed. Additional tests may be needed if infection or a tumor is suspected [1].

Sampling the Lump

If the lump is not a simple impaction, your vet will likely recommend a fine needle aspirate or a biopsy. A biopsy gives a tissue diagnosis, which is the only way to tell a benign polyp from a carcinoma. In the reported cat with anal sac gland carcinoma, the diagnosis came from microscopic evaluation of the excised mass [2].

Staging Tests

If cancer is confirmed, staging looks for spread. Blood work, chest imaging, and abdominal ultrasound are common. Lymph node involvement and lung metastasis have both been documented in cats with anal sac adenocarcinoma [5][6]. Finding spread early changes the treatment plan.

Treatment Options

Treatment depends on what the lump is.

Impacted or infected sacs are usually emptied and flushed, with antibiotics if infection is present.
Abscesses may need to be lanced and drained, plus pain medication.
Benign polyps and adenomas can often be removed through the anus or with an endoscope, and removal is often curative [4].
Malignant tumors usually need more aggressive surgery, such as a rectal pull-through, to get clean margins [4].
Some cats with anal sac cancer receive chemotherapy or radiation. One cat with squamous cell carcinoma of the anal sac was treated with surgery, radiation, and toceranib phosphate, then carboplatin when the tumor came back locally [3]. Another cat with recurrent anal sac adenocarcinoma had a partial response to carboplatin but a short duration of response [6].

Your vet will calculate any drug dose from your cat's weight and health. Never give human pain relievers to a cat, because many are toxic.

If your cat has a lump in the ear canal instead of the rear end, the same principle applies, get it identified. Ear Polyps in Cats: Signs, Diagnosis, Surgery, and Recurrence walks through that process.

Prevention and Monitoring

You cannot prevent every lump, but you can catch problems early.

Check your cat's rear end once a month. Look for swelling, redness, dark spots, or discharge.
Keep up with routine wellness exams. Your vet can feel the anal sacs during a normal visit.
Watch for scooting, licking, or straining. These are the earliest signs of anal sac trouble [1].
If your cat has had an anal sac mass removed, follow the recheck schedule closely. Local recurrence has been reported after surgery for anal sac cancer [3].
Track any new lump with a photo and a date. Growth over weeks matters more than size on any single day.

Limitations and When to Contact a Veterinarian

No article can tell you what a specific lump is. Only a veterinarian who examines your cat and possibly samples the tissue can do that. Use these timing guidelines.

Emergency now: heavy bleeding, a ruptured mass with fever or lethargy, inability to poop, severe pain, or new weakness in the back legs.
Same day or next day: a fast-growing lump, a dark or blood-filled bump, an open draining sore, or a cat that will not eat.
Within a few days: a firm lump that is not painful, mild scooting, or occasional straining to poop.
Routine visit: a small stable lump found during home checks with no other signs.

When in doubt, call your vet and describe what you see. A phone call costs nothing and can save time.

Frequently Asked Questions

Is a bump on my cat's anus always cancer?

No. The most common anal sac problem in cats is impaction, which is not cancer [1]. Abscesses and benign polyps are also common. That said, malignant tumors of the anal sac do occur in cats, so any lump deserves an exam [2][3].

Can I pop an anal gland abscess at home?

No. Do not squeeze or lance it yourself. An abscess can be deep, and rupturing it at home risks spreading infection and causing serious pain. Your vet can drain it safely and prescribe appropriate treatment.

What does a cat tumor on the anus look like?

It often looks like a firm swelling beside the anus that may be painful to touch. In one reported cat, the mass was a firm, painful swelling in the perianal region that turned out to be anal sac gland carcinoma [2]. Some tumors ulcerate or bleed, and some are dark in color.

Why does my cat have a white bump on the anus?

A white or pale bump may be a blocked gland, a small cyst, or a benign growth. Color alone does not tell you what it is. Your vet may need to sample it to know for sure.

How fast do anal sac tumors grow in cats?

Growth rates vary, and there is no single timeline that applies to every cat. Some cats show local recurrence months after surgery, as seen in one treated case where the tumor returned at 236 days [3]. This is why recheck exams after treatment matter so much.

References

Disorders of the Rectum and Anus in Cats - Cat Owners. Merck Veterinary Manual.
Anal sac gland carcinoma in a cat. Veterinary pathology, 2006.
Squamous cell carcinoma of the anal sac in two cats. The Journal of small animal practice, 2021.
Rectal Neoplasia in Dogs and Cats - Digestive System. Merck Veterinary Manual.
Apocrine gland anal sac adenocarcinoma with perineural metastasis in a cat. JFMS open reports, 2018.
Carboplatin chemotherapy in a cat with a recurrent anal sac apocrine gland adenocarcinoma. Journal of the American Animal Hospital Association, 2010.
Deep dermal and subcutaneous canine hemangiosarcoma in the perianal area: diagnosis of perianal mass in a dog. BMC veterinary research, 2019.