Perianal Adenoma vs Perianal Adenocarcinoma

Painted illustration of perianal gland tumors in a dog

What is it?

Hepatoid (perianal) glands are modified skin glands found around the anus and also on the prepuce, tail base, groin, inner thigh, and back; only dogs have them. Tumors of these glands are mostly benign adenomas, which make up 58 to 96% of tumors in this area. Adenocarcinomas are the uncommon malignant form. Testosterone promotes these tumors, so they are far more common in unneutered males and rare in neutered males. Breeds at higher risk include Siberian huskies, cocker spaniels, Pekingese, Shih Tzus, Lhasa apsos, German shepherds, and Samoyeds.

What signs should I watch for?

Adenomas are usually one or more small, round, pink, hairless, slow-growing bumps around the anus, prepuce, scrotum, or under the tail. They may ulcerate and become infected, and your dog may lick the area. Adenocarcinomas look similar but tend to grow faster and larger, are more often multiple, and can press on the rectum, causing straining and constipation. Some cause high blood calcium, leading to increased thirst and urination, poor appetite, weight loss, weakness, and vomiting.

Here is how the two compare:

	Perianal adenoma	Perianal adenocarcinoma
Behavior	Benign (not cancer)	Malignant (cancer)
How common	Most common perianal tumor (58 to 96%)	Uncommon
Who gets it	Mostly unneutered male dogs; rare in neutered males	Also mainly unneutered males, but can occur in any dog
Growth	Slow; usually under 1 inch (2.5 cm)	Fast; can reach about 4 inches (10 cm) and invade deeper tissue
Spread	Does not spread	Can spread to lymph nodes, abdominal organs and lungs
Other effects	May ulcerate and become infected	Straining or constipation; high blood calcium in about 30 to 50% (thirst, urination, weakness)
Main treatment	Neutering plus removal of the tumor	Wide surgical removal, often of nearby lymph nodes, plus neutering; radiation or chemotherapy
Outlook	Good; recurs in under 10% after neutering and removal	Fair to guarded

How is it diagnosed and treated?

Because the two can look the same, a fine needle sample, biopsy, or full removal of the lump is needed for a diagnosis. Adenocarcinomas are sometimes found only on a rectal exam. For adenomas in intact males, neutering plus tumor removal is the treatment of choice, and small tumors often shrink after neutering. For adenocarcinomas, complete surgical removal (sometimes with nearby lymph nodes) and neutering are recommended, often with radiation or chemotherapy, after staging tests such as bloodwork, chest X-rays, and abdominal ultrasound.

Can it be prevented, and what's the outlook?

Neutering greatly lowers the risk of these tumors.
The outlook for adenomas is good, with recurrence under 10% after neutering and removal.
Adenocarcinomas have a fair to guarded outlook because they can regrow and spread.
Have any lump near the anus checked promptly.

Reviewed by the Adler Veterinary Hospital veterinary team, October 2026.

Older unneutered male dogs; huskies, cocker spaniels, Shih Tzus

Who's at risk:

Pink lumps around the anus, licking, straining to defecate

Main signs:

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Urgency:

When to call a vet right away