What are hepatoid gland tumors?
Hepatoid gland tumors are a type of cancer that develops from the disorganized and uncontrolled production of hepatoid gland cells. Hepatoid glands are modified sebaceous (sweat) glands of the skin, and are located in the perianal area (around the anus), as well as the prepuce, base of the tail, groin, inner thigh, and the back. These glands only occur in dogs. The tumor cells resemble liver (hepatic) cells, hence the name.
The most common location for these tumors is the perianal area. The three main types of tumors that occur in the perianal area are adenomas (benign), adenocarcinomas (malignant, or cancerous), and epitheliomas (borderline malignant).
Perianal adenomas account for 58%-96% of all tumors in the perianal area. These tumors occur most commonly in intact (unneutered) dogs and are the third-most common type of tumor in intact male dogs. Adenocarcinomas are uncommon and epitheliomas are rare.
What causes this cancer?
The reason why a particular dog may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.
A risk factor for hepatoid gland tumors is hormones, specifically testosterone and estrogen. Both hormones are associated with tumor development and growth. Since testosterone promotes these tumors, perianal adenomas and adenocarcinomas are much more common in unneutered male dogs than female dogs, and are rare in neutered males. Since estrogen inhibits these tumors, they are more common in spayed female dogs than unspayed female dogs. These tumors are also associated with other types of cancer (e.g., testicular and adrenal gland tumors) and Cushing’s disease (hyperadrenocorticism).
Hepatoid gland tumors are more common in certain breeds, such as Siberian husky, cocker spaniel, Pekingese, shih tzu, Afghan hound, lhasa apso, German shepherd, and Samoyed.
What are the signs of these tumors?
The signs of hepatoid gland tumors vary depending on whether they are benign or malignant. In the case of benign perianal adenomas, you may see one or more small, round, pink, hairless, slow-growing nodules around the anus. Although they usually grow around the anus, they can grow in the prepuce, scrotum, and under the tail. Occasionally, they will ulcerate (break open) and become infected. In this case, they may become irritated and painful, and you may notice your dog frequently licking the area.
Adenomas and adenocarcinomas look alike, but adenocarcinomas typically grow more rapidly and can become much larger; up to 4 inches (10 cm) in diameter. It is more likely there will be multiple adenocarcinomas. They may also spread to the lymph nodes and underlying tissue, so they can compress the rectum, causing your dog to have difficulty defecating (straining) and constipation.
Adenocarcinomas can also cause a condition called paraneoplastic hypercalcemia (tumor-related high blood calcium). This condition occurs in about 30%-50% of dogs with adenocarcinoma. If your dog has hypercalcemia, you may notice increased drinking and urination, loss of appetite, weight loss, lethargy, weakness, vomiting, and constipation.
How are these tumors diagnosed?
Your veterinarian may suspect a hepatoid gland tumor by its typical outward appearance or by feeling a mass (or enlarged lymph nodes) while performing a rectal palpation. Perianal adenocarcinomas may be found incidentally, via rectal palpation, with no outward signs of disease.
"Your veterinarian may suspect a hepatoid gland tumor by its typical outward appearance or by feeling a mass (or enlarged lymph nodes) while performing a rectal palpation."
Diagnosing a suspected tumor requires a microscopic examination of the tissue. Your veterinarian may use one or more methods to obtain a tissue sample for diagnosis. The most common methods include fine needle aspiration (FNA), biopsy, or full excision of the tumor.
Fine needle aspiration (FNA) involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope. In some cases, results from FNA may not be entirely clear and a biopsy may be necessary.
A biopsy is a surgical excision of one or more pieces of the tumor. The pieces are then examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is helpful in making a diagnosis, and can also indicate how the tumor is likely to behave. Alternatively, the tumor may be fully excised and sent for histopathology.
How does this cancer typically progress?
Perianal adenomas typically grow slowly and usually to a size of less than 1 inch (2.5 cm). Epitheliomas behave like adenomas except they may infiltrate the surrounding tissues. Adenomas and epitheliomas are prone to ulceration and infection.
Perianal adenocarcinomas typically grow rapidly, invade the underlying tissues, and can spread (metastasize) to the local lymph nodes, abdominal organs, and lungs. Tissue invasion and lymph node involvement can lead to difficulties with defecation. Metastasis to the other organs can damage these organs, and lead to systemic illness, lethargy, and weight loss.
Staging (searching for potential spread to other locations in the body) is highly recommended for adenocarcinomas. Staging may include bloodwork, urinalysis, radiographs (X-rays) of the lungs, and possibly an abdominal ultrasound. If any lymph nodes are enlarged or feel abnormal, further sampling may be pursued to determine if spread is present.
What are the treatments for these tumors?
Treatment depends on the tumor type, size, and malignancy, as well as the presence of metastasis. Treatment typically involves several options, including surgical removal of the tumor along with neutering (in male dogs), cryotherapy, laser ablation, radiotherapy, chemotherapy, and occasionally hormone therapy.
For most perianal adenomas, the treatment of choice in intact male dogs is castration and tumor removal. Small tumors often get smaller after neutering or do not progress. If the tumors are not ulcerated, they may not require surgical removal.
If there are many tumors, or if the tumors are large or spread out or close to the anal sphincter, it may be advisable to neuter first and wait several months before removing the tumors. Without the influence of the hormone testosterone (from the testes), the tumors will shrink, making their removal safer and easier. The surgical removal of adenomas is recommended in female dogs and neutered male dogs.
When adenomas are smaller than 1–2 inches (2.5-5 cm) in diameter, cryotherapy or laser ablation may be used to remove them. If adenomas reoccur after neutering and tumor removal, a second biopsy to rule out an adenocarcinoma is strongly recommended, along with testing for underlying hyperadrenocorticism.
For perianal adenocarcinomas, the treatment of choice is complete surgical excision of the tumor (sometimes with removal of the nearby lymph nodes) and neutering. Radiation or chemotherapy is recommended for these types of tumors. With successful therapy, high blood calcium levels will return to normal.
What is the prognosis for hepatoid gland tumors?
The prognosis for perianal adenomas is good with neutering and tumor removal: they recur at a rate of less than 10%. Without neutering, the adenomas commonly regrow, and new tumors develop. The prognosis for epitheliomas is generally good. They will occasionally regrow.
The prognosis for perianal adenocarcinomas is fair to guarded because of the potential for tumor regrowth, tissue invasion, and metastasis (spreading). For dogs that initially present with hypercalcemia, your veterinarian will monitor the blood calcium levels, as rises can indicate tumor recurrence or metastasis. Your veterinarian and veterinary oncologist will provide guidance on the best treatment options to achieve the best possible outcomes.
