Sebaceous adenoma in dogs: gland lumps and cysts

Overview

Sebaceous glands secrete sebum into hair follicles and onto the skin. Tumours and tumour-like changes arising from them are common in dogs. Sebaceous hyperplasia, or gland overgrowth, is an age-related change. It often appears as small raised skin bumps.

Hyperplasia is rarely larger than 1 cm. An adenoma resembles it but is often more than 1 cm across. Size does not replace examination of cells or tissue. An epithelioma is a sebaceous tumour containing many immature precursor cells. Sebaceous adenocarcinoma is a rare malignant form.

A cyst is a cavity containing fluid or more solid material, rather than a mass of tumour cells. A sebaceous cyst contains sebum. A follicular cyst can contain keratin, the skin's horny material. A bump described as a sebaceous lump is therefore not necessarily a sebaceous gland tumour.

A sebaceous hamartoma noticed immediately after birth may be about 5 cm long or wide. It is typically a single elongated or rounded growth. Sebaceous lesions therefore include lumps with a different developmental background from an older dog's small adenomas.

Causes

A sebaceous tumour develops from disordered growth of cells belonging to the gland. The exact cause in an individual dog is unknown. Environmental and inherited factors can generally contribute to tumour risk. This does not mean one care decision by an owner explains why a lump formed.

A follicular cyst can develop when a follicle opening becomes blocked or the follicle is damaged. Mechanical injury and ultraviolet sunlight can contribute to cyst formation. A sebaceous cyst forms in the region of a sebaceous gland associated with a hair follicle. A true cyst has a secretory cell lining on its inner surface. This structure affects how recurrence is prevented during removal.

Not every cyst-like cavity has a secretion-producing wall. Such a false cyst can form after bleeding or a blow that damages tissue. Its fluid may result from liquefaction of dead tissue. This differs from the formation of a cyst in a sebum-producing gland.

Risk factors

Sebaceous adenoma is common particularly in older dogs. Susceptible breeds include Cocker Spaniels, Samoyeds and Alaskan Malamutes. Sebaceous hyperplasia is also associated with old age. Susceptible breeds include Manchester Terriers, Soft Coated Wheaten Terriers and Welsh Terriers.

Malignant sebaceous tumours are usually seen in middle-aged and older dogs. Susceptible breeds include Cavalier King Charles Spaniels, Cocker Spaniels, Scottish Terriers, Cairn Terriers and West Highland White Terriers. Males may be more susceptible. These susceptibilities relate to particular tumour groups, rather than a shared risk distribution for every skin lump.

Inherited susceptibility to recurring follicular cysts has been described in Boxers, Shih Tzus, Schnauzers and Basset Hounds, for example. Other breeds can also be affected. Even a young dog may develop several recurring follicular cysts on the head. A glandular hamartoma noticed after birth differs from an older dog's ordinary adenoma.

Blackheads associated with follicle blockage can also be linked to corticosteroid treatment, an underactive thyroid, Cushing's disease or allergy. In hairless breeds, inactive follicles may promote follicular cyst formation. Blackheads can develop at pressure points in thin-coated dogs with little body fat.

Typical symptoms

Sebaceous adenomas may be multiple and often develop on the head. However, any skin area can be affected. Some cause little trouble for the dog. Features you may notice at home include:

• A firm or raised skin nodule.
• A shiny or keratinised surface over a hyperplastic growth.
• A crust forming over an adenoma.
• Surface inflammation or ulceration.
• Increased licking or biting of an irritated area.
• A pale or bluish cyst-like swelling.

When a sebaceous cyst ruptures, greyish, brown or cottage-cheese-like material may drain out. Follicular cysts can smell unpleasant because of secondary bacterial or yeast infection.

Sebaceous cysts occur particularly on the head, neck, trunk and upper limbs. Hair may be lost over a cyst. A blood-filled false cyst can look dark. An epithelioma often appears as an ulcerated nodule several centimetres in diameter.

Complications and consequences

Bacterial skin infection can develop on a sebaceous adenoma's surface. Licking and scratching cause further skin damage. A lump at the eyelid margin can rub against the cornea and cause an ulcer. The skin growth then affects eye health and is more than a cosmetic lump.

A follicular cyst rupturing within the skin can cause inflammation and pain. A sebaceous cyst can also develop secondary bacterial infection. Residual tissue from even a benign tumour can regrow at the surgical site. New adenomas appearing elsewhere later are also common.

The outlook for epithelioma is usually good. Local recurrence has been estimated in about 6% of treated cases. Rare adenocarcinoma can invade surrounding skin. It can spread to regional lymph nodes later in the disease. The precise tumour classification therefore affects prognosis and follow-up needs.

Local recurrence of sebaceous hyperplasia has been estimated in about 1.1% of cases. New hyperplastic growths may develop elsewhere in up to 10%. Local recurrence and a new lump at another site are therefore separate things to monitor.

Diagnosis at the vet

Classification of adenoma and epithelioma considers how mature the gland cells are. Epithelioma lobules may extend deep into the dermis. This growth pattern can make it harder to distinguish from a malignant sebaceous tumour. A wart-like surface therefore does not reveal the whole structure of a skin lesion.

The vet assesses the lump's size, texture, shape, location and signs of inflammation. Fine-needle sampling collects cells for microscopic examination. A pathologist examines them on a slide. However, a sample containing abundant gland secretion does not always provide enough diagnostic information.

A biopsy or removal provides tissue whose structure a pathologist can also assess. This tissue examination is called histopathology. It helps with both diagnosis and assessment of tumour behaviour. Tissue examination of a cyst can establish whether its wall was removed completely.

An inflamed or ulcerated appearance does not distinguish benign epithelioma from a malignant sebaceous tumour. Nor does an earlier lump's diagnosis identify a new growth. Cyst contents can be sampled, but definitive identification may require tissue. Recurring or multiple cysts may require investigation of an underlying cause.

Treatment

The vet prescribes treatment and medicines. A confirmed benign sebaceous tumour does not always need removal if it neither becomes inflamed nor troubles your dog. Removal is considered with growth, irritation or an awkward location. Removed tissue is sent to a pathologist to confirm the tumour type.

Surgical removal is the usual treatment for a cyst. Preventing recurrence requires complete removal or destruction of its inner lining too. Laser treatment can be used for some true cysts. Topical treatment may help with multiple small follicular cysts. The approach therefore depends on whether the lesion is a gland tumour or a cavity within the skin.

Surgery is the first-choice treatment for malignant adenocarcinoma. Complete removal may be difficult when the tumour invades surrounding tissues. Additional radiotherapy is considered when needed. There is no established chemotherapy protocol for these growths. A difficult case may require a vet with expertise in skin disease or cancer treatment.

After surgery, prevent wound licking with a collar or protective clothing. Avoid running and jumping to reduce wound strain. Exercise is restricted for 7–10 days after many skin operations. Removable skin sutures are usually taken out after 7–14 days, depending on the procedure.

A trauma-related false cyst may shrink over time without surgery. Retinoids have been considered for preventing sebaceous hyperplasia recurrence, but their use is not established. Assessing suitability requires specialist expertise.

The skin may be irritated after needle sampling or surgery. The vet can prescribe pain relief for pain and inflammation after biopsy or surgery.

Prevention

No single known cause of sebaceous tumours exists, so you cannot target prevention at one clear factor. Regular skin checks help identify new bumps early. Feel the head, legs and tail areas too. A new lump is not identified from an old adenoma's diagnosis.

Rubbing, scratching and biting a cyst can cause inflammation and bleeding, so preventing these reduces local problems. If the underlying cause of cysts can be removed, some may shrink or disappear. With breed-associated cysts, susceptibility to new growths may persist.

Important for dog owners

Record the date a lump was found, its location and size. Take a photograph including surrounding skin so you can find the same spot later. Note separately which lump the vet sampled and the diagnosis received. Monitor surface changes, pain and discharge as part of follow-up. This helps keep old and new lumps on different body areas distinct.

Do not squeeze or puncture a cyst at home, as this can worsen inflammation. If the surface opens, keep it clean and protect it as advised by the vet when needed. Keep a surgical wound clean and dry. Contact the veterinary team if swelling increases markedly or a suture comes out.

Chewing a wound can remove a suture or damage the surgical site within seconds.

Frequently asked questions

Is a sebaceous adenoma the same as a wart?

No. A sebaceous adenoma arises from a skin sebaceous gland. A papilloma wart is a viral skin growth. A wart-like appearance does not identify the cells' origin, so show a new or changing lump to a vet. Sampling helps with diagnosis and treatment planning.

Must a symptom-free adenoma always be removed?

A confirmed benign sebaceous tumour can often be monitored if it is not inflamed or causing problems. An awkward location, growth or persistent irritation may change the situation. Monitoring is agreed only after examination and assessment of tumour type.

Why does a cyst refill after emptying?

A true cyst has a secretion-producing inner lining. Preventing recurrence may require complete removal or destruction of this layer. Simply squeezing out discharge and other contents therefore does not address the cyst's structure, and squeezing at home may increase inflammation.

Can even a benign lump endanger an eye?

Yes. A tumour at the eyelid margin can rub the eye and cause a corneal ulcer. Your dog may squint or rub the face. A dog with eye signs needs prompt assessment even if the skin tumour was previously confirmed benign.

Does a new lump mean cancer has spread?

Not necessarily. A dog with sebaceous hyperplasia or adenoma can develop new growths at other sites later. The new lump's type still needs separate assessment, as the previous diagnosis does not guarantee it is the same.