Vancouver Feline Hospital - Cat Veterinary Clinic

Because these are nasty cancers, the diagnostic process is often combined with the treatment process as follows:

1. Physical examination
2. If only one gland involved, or small lumps - presurgical minimum data base and then do surgical excision and biopsies of lumps and associated lymph nodes. Surgery can be curative on smaller cancers - so there is no point in waiting. No fine needle aspirate. Consider chemotherapy only if clean margins not achieved or if spread to lymph nodes on histopathology.
3. If multiple glands or large ulcerated lumps, minimum data base. If metastases evident, palliative care - consider NOT doing surgery in this case. Fine needle aspirate may be all the confirmation you need.
4. If large and no metastases evident, consider surgical excision and chemotherapy.
   

Treatment: (Longer description further on in article)

1. Initial treatment is surgery - taking out the entire mammary chain and related lymph nodes with wide surgical margins.
2. Chemotherapy with doxorubicin improves survival. Other chemotherapy drugs can be used. Radiation therapy may help.
3. Supportive - pain control, nutritional support, nursing care.
   

Survival times:

• Best (small tumour, no evidence metastases) - about 3 years
• Worst (large tumour, metastases) - 1-2 months
• Treatment chosen depends on you, your cat, and the stage of the cancer.

Medical Information

Incidence

• Most common - epithelial, then adenocarcinomas, solid carcinomas
• Rare - mixed mammary tumours, sarcomas (also slow to metastasis)

Signalment

• Older cats (median 10-12yrs), as young as 2yrs, as old as 20yrs
• Risk in un-spayed female cats increases steadily with age; although one study suggests that early spaying halves the risk, other studies have not been as optimistic.
• Progestin treatment in either sex will increase risk.(In captive non-domestic felids, tumors were more frequent in cats exposed to melengesterol acetate, but duration of exposure or higher cumulative doses did not seem important).
• Spontaneous mammary carcinoma has occurred in male cats.
• DSH and DLH most common (most common "breed"), tricolour cats may be increased risk (12% cancers but 7% population)
• Siamese predisposed (22% cancers but 5% population)

Etiology

• 1970's - thought a retrovirus involved - studies failed to show evidence - viral cause unlikely.
• Progesterone and oestrogen receptors involved (less than in benign tumours). Feline breast tissue does not routinely express high oestrogen receptor levels. Progesterone receptors are expressed at significant levels in feline mammary cancer. The reason and significance of this is unknown but it does influence treatment options (tamoxifen, an anti-oestrogen, is not likely to be effective in cats). High progesterone levels clearly defined risk factor in non-domestic Felids, role may be clouded in domestic cats but still considered major risk.
• The feline BRCA1 gene has not been identified to date so the contribution of mutations to this gene to the overall incidence of breast cancer in cats is unknown.

Clinical Behavior

Approximately 85% of feline mammary neoplasms are histologically malignant. Cancer may arise from either glandular or ductal tissue and tumors are categorized as either solid (35%), tubular (50%), or papillary (15%). Fifty percent of cats may have multiple glands develop tumors simultaneously. Local extension may be significant with rapid spread to regional lymph nodes and a relatively high rate of distant metastasis if not detected and treated early.

Tummy rubs are often not a petting option in most cats - these tumours are often detected late, then left to sit to long before presentation to the veterinarian. Veterinarians who understand the nature of these cancers will attempt to have the lump and lymph nodes surgically excised within a week of presentation.

Cats have four mammary glands on each side (three thoracic and one abdominal), with greater lymphatic anastomosis between the thoracic and abdominal lymph drainage than in dogs, although there does not appear to be lymphatic anastomosis across the midline.

Tumours are more likely to occur in the third and fourth mammary glands. The regional lymph nodes may not be enlarged but may still contain tumour cells - do not neglect to biopsy! Widespread metastasis can cause significant morbidity related to anorexia, dyspnea, coughing, neurological signs. Bone and eye metastasis are occasionally involved.

(In non-domestic felids, these tumours are typically very widespread when first presented and many will have metastasied to the bone - seen on x-ray as a primarily osteolytic without obvious periosteal reaction. Abdominal radiology is not very sensitive when looking for mets to abdominal organs).