Adenocarcinoma in Dogs

Adenocarcinoma in dogs is one of the most common types of cancer, being the most common primary cancer of the colon, kidney and rectum. An adenocarcinoma is a malignant growth of the glandular tissue cells most often originating from the uterus, anus, intestines or mammary glands. Often they metastasize or spread to the lungs; 80% of all lung tumors are adenocarcinomas. They can also spread to the liver and other abdominal organs. This cancer can also originate in the perianal area: the sebaceous glands in males and the anal sacs or mammary glands in females.

Causes of Adenocarcinoma

Adenocarcinomas occur in the mammary glands of older non-spayed female dogs whereas the cancer appears in the perianal area of males, including the scrotum, prepuce and tailhead. Rarely does the cancer develop in the prostate, mammary tissues or anal sacs of males. Females with anal sac adenocarcinomas have a worse prognosis than males with the disease appearing elsewhere because cancer of the anal sac is more invasive, more aggressive, spreads quickly and results in a high calcium blood level leading to kidney damage. Males with adenomas (benign tumors) appearing in the perianal area can be resolved with castration.

Though anal sac adenocarcinoma is a less common form of cancer than the mammary glandular form, it can quickly spread to the lymph nodes thereby affecting the entire body of the diseased dog.

Symptoms of Adenocarcinoma

Though swelling, pain and loss of appetite followed by weight loss is common to both mammary tumors and anal sac adenocarcinomas, there are some differences.

Dogs with mammary tumors will exhibit:

  • Weakness or fatigue
  • Swelling in the hind legs
  • Sudden appetite loss
  • Sudden weight loss
  • Painful, inflamed or ulcerated mammary skin
  • One or several tumors forming a mass underneath the abdominal skin

Dogs with adenocarcinoma(s) in the perianal area including the anal sac will exhibit:

  • Inflammation in the perianal region
  • Excessive licking of the perianal region
  • Loss of appetite
  • Weight loss
  • Constipation
  • Discomfort in passing stools or eliminating ribbon-like stools
  • Blood in the stools
  • High blood calcium levels resulting in kidney failure

Dogs with adenocarcinomas occurring elsewhere in the body (kidney, lungs, liver, brain, bones, spleen, lymph nodes) may exhibit:

  • Blood in the urine (kidney cancer)
  • Increased frequency in urinating
  • Increased thirst
  • Abdominal distention 
  • Coughing or labored breathing indicating the cancer has spread to the lungs

Diagnosis and Treatment of Adenoarcinomas in Dogs

Adenocarcinomas cannot be cured; however, treatment can improve the quality of life for any dog diagnosed with the disease. A veterinarian will conduct a complete physical exam (palpation of the lymph nodes and a digital rectal exam), blood tests (blood count and serum chemistry), x-rays and or an ultrasound of the abdominal area and possibly a fine-needle aspirate biopsy, which does not require surgery.

Mammary tumors and anal sac adenocarcinomas usually require the surgical removal of the tumors followed by chemotherapy or radiation. If the kidneys are affected, then treatment of the high calcium levels to promote kidney function would be recommended. Depending upon how early the cancer was detected and how far it has spread determines the prognosis of the disease.