Mammary Gland Tumor in Cats

Over 85 percent of mammary tumors in cats are malignant and they tend to grow and metastasize quickly. Like breast tumors in humans, they start as a small lump in a mammary gland. Often, more than one mammary gland is affected. This disease is preventable by having female cats spayed before six months of age. 

Symptoms and Types

Mammary gland tumors begin as masses underneath the skin. However, over time they can become aggressive and ulcerate the skin. Cats tend to lick and groom the area excessively, and a strong odor can result as the tumor becomes necrotic and infected. General signs of ill health like anorexia or depression are often seen as the disease progresses. 


A fine needle aspirate is typically the tool used to determine whether a small mass is a mammary tumor. An incisional biopsy may also be discussed, but if a fine needle aspirate does not fully diagnose the tumor, complete removal, including wide margins of tissue around the mass, may be recommended due to a high rate of malignancy in cats. A fine needle aspirate of nearby lymph nodes may also be recommended to determine if the mass has metastasized. Radiograph X-rays of the thorax and an ultrasound of the abdomen may determine metastasis to the lungs or other internal tissues. 

Because the cat is usually middle aged or older at the time of diagnosis, additional blood work may also be recommended to further determine diagnosis and treatments. 

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