Feline Mammary Gland Tumors
Feline mammary gland tumors (MGT) are the 3rd most common tumor in cats. It has been shown that spaying animals when they are young can decrease the formation of MGTs in both cats and dogs. Up to 85-90% of feline MGT are malignant. The most common type is an adenocarcinoma (tubular, papillary, solid, ductular). They are often noted in cats during a physical exam or by the owner through grooming of the pet. In many cases, the tumors are in an advanced stage by the time they are brought to the veterinarian. The mass may be firm and can be ulcerated.
In order to work up a cat with MGT, staging is performed to determine where else the tumor may have spread. This involves bloodwork (CBC, serum chemistry), chest radiographs, an abdominal ultrasound and possibly lymph node aspirates.
Treatment for MGT includes the use of surgery and chemotherapy. Mammary masses should be surgically removed as aggressively as possible. It has been shown that more radical resection (unilateral or bilateral resection) offers a better chance of removing all of the cancer than simply removing that one gland since this type of cancer can spread through the lymphatics. All tumor tissue and associated lymph nodes should be removed and submitted for biopsy. Chemotherapy after surgery involves the use of adriamycin +/- carboplatin. One treatment is given every three weeks for 4-6 total treatments. Prior to receiving adriamycin, cats need to have the kidneys examined because this drug in some cases can cause kidney damage, especially if given many times. Most cats tolerate this protocol very well. With the addition of chemotherapy, a patient’s survival time can be increased over surgery alone.
Prognosis depends upon many factors and they include:
1. Type of surgery: Most conservative surgeries have cancer recurrence vs radical surgeries.
2. Size of tumor: Tumors >3cm have a median survival time of 4-5 months, Tumors 2-3 cm have a median survival time of 1-2yrs, and less than 2cm are over 3yrs.
3. Lymph node metastasis: Spread to a lymph node at the time of surgery is a poor prognostic indicator because it means the cancer has already spread.
4. Tumor grade: High-grade tumors are worse than low-grade tumors.
5. Chemotherapy plus surgery can help prolong survival in cats.