What are hepatoid gland tumors?
Hepatoid gland tumors are a type of cancer that develop from the disorganized uncontrolled proliferation of the cells of hepatoid glands. Hepatoid glands are modified sebaceous (sweat) glands of the skin located in the perianal (around the anus) area, 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.
Hepatoid gland tumors account for approximately 10% of all cases of skin cancer diagnosed in dogs. The most common location for these tumors is the perianal area. The three main types of tumors that occur in the perianal area include adenomas (benign), adenocarcinomas (malignant) and epitheliomas (borderline malignant).
Perianal adenomas account for 80% of all tumors in the perianal area. They occur most commonly in intact (unneutered) dogs and are the third most common type of tumor in unneutred 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 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 females) and are rare in neutered males. Since estrogen inhibits these tumors, they are more common in spayed female dogs than those that are unspayed. These tumors are also associated with other types of cancer (e.g., testicular and adrenal gland tumors) and Cushing’s Disease (hyperadrenocorticism).
"A risk factor for hepatoid gland tumors is hormones, specifically testosterone and estrogen."
These tumors are more common in certain breeds. Perianal adenomas are more common in Siberian Huskies, Cocker Spaniels, Pekingese, and Samoyeds. Perianal adenocarcinomas are more common in Siberian Huskies, Bulldogs, and Alaskan Malamutes.
What are the signs of these tumors?
The signs of these tumors vary depending on whether they are benign or malignant. In the case of benign perianal adenomas, you many 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” (10 cm) in diameter. It is more likely that there will be multiple adenocarcinomas. Because they may also spread to the lymph nodes and underlying tissue, 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. 35-40% of perianal adenocarcinomas are found incidentally via rectal palpation, with no outward signs of disease.
The diagnosis of a suspected tumor requires a microscopic examination of the tissue. Your veterinarian may use one or more methods of obtaining a tissue sample for diagnosis. The most common methods include fine needle aspiration (FNA), biopsy, or full excision of the tumor.
"In some cases, results from FNA may not be entirely clear and a biopsy may be necessary."
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 not only helpful to make a diagnosis but can 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 only to a certain size, usually less than 1 inch (3 cm). Epitheliomas behave like adenomas except that 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. This 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?
The choice of treatments for these tumors depends on the type, size, and malignancy of the tumor, 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."
For most perianal adenomas, the treatment of choice in intact male dogs is castration and tumor removal. Small tumors frequently regress after neutering or do not progress, and if not ulcerated, may not require surgical removal. If the tumors are large or multiple (and spread out) or close to the anal sphincter, it may be advisable to neuter first and wait several months before removing them. Without the influence of the hormone testosterone (from the testes), the tumors will shrink in size making their removal safer and easier. The surgical removal of adenomas is indicated in female and neutered male dogs.
When adenomas are smaller than 1 to 2 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, the high blood calcium level will return to normal.
Is there anything else I should know?
The prognosis for perianal adenomas is good with neutering and tumor removal. Recurrence rates are <10%. Without neutering, the adenomas will commonly regrow, and new tumors develop. The prognosis for epitheliomas is generally good. Occasionally they will regrow.
The prognosis for perianal adenocarcinomas is fair to guarded because of the potential for tumor regrowth, tissue invasion, and metastasis. For dogs that initially present with hypercalcemia, your veterinarian will monitor the blood calcium levels, as rises can indicate tumor recurrence or the presence of metastasis. Your veterinarian and veterinary oncologist will provide guidance on the best treatment options to achieve the best possible outcomes.