[Written by a Veterinarian] What is feline mammary cancer? Symptoms, causes, treatment, and preventive measures you can take.

When you "feel a lump in your cat's abdomen or breasts," one disease that comes to mind is feline mammary cancer. Feline mammary cancer progresses rapidly, and if detected late, the risk of metastasis increases. Therefore, early detection and appropriate action can save your cat's life. In this article, veterinarians explain in detail, based on their actual clinical experience, everything from symptoms to treatment and prevention.

What is Feline Mammary Cancer?

What kind of disease is mammary cancer?

Feline mammary cancer is a malignant tumor that develops in a cat's mammary glands. While tumors in a cat's mammary glands can be benign or malignant, approximately 90% of feline mammary tumors are malignant mammary cancers. Mammary tumors, including mammary cancer, are the third most common type of tumor in cats. They progress very rapidly, spreading (infiltrating) to the skin and abdominal wall, and can metastasize to nearby lymph nodes or distant organs such as the lungs and liver. In my own experience, it is such a fast-progressing tumor that lymph node metastasis was confirmed near the primary tumor at the time a single mammary cancer was identified.

Age and Gender Most Affected

The age at which mammary cancer develops varies widely, from 9 months to 23 years. The most common age of onset is 10-12 years. Since sex hormones are involved in the development of mammary cancer, it occurs almost exclusively in female cats. It is said to be common in Siamese cats, with Siamese cats having twice the risk of developing it compared to other cat breeds.

Risk Factors (Presence of Spaying/Neutering, Relationship with Hormones)

Mammary cancer is related to sex hormones, and the incidence rate changes depending on whether spaying/neutering has been performed. If spaying is performed around 6 months of age before the first estrus, the risk of developing mammary cancer decreases by approximately 90%. However, the incidence rate increases with repeated estrus cycles. In cats, spaying does not guarantee complete prevention, and in my experience, I have seen mammary cancer in cats spayed at 6 months of age. However, it is known that spaying performed early has a significantly higher preventive effect.

Symptoms and Detection of Feline Mammary Cancer

Lumps and Swelling

Mammary cancer is a malignant tumor that forms in the mammary glands. Therefore, lumps can form near the nipples, or the surrounding area may become hard and swollen. This can occur on one side only, but it can also affect both mammary glands.

Bleeding, Ulcers, Skin Irritation

Because a cat's tongue is rough, they may excessively lick the area of mammary cancer, leading to bleeding, ulcers, and skin irritation. In advanced mammary cancer, tumor cells and blood vessels spread to the skin, causing bleeding and other symptoms. Additionally, there is a dramatically progressive type of mammary cancer called inflammatory mammary carcinoma. Inflammatory mammary carcinoma can cause the skin of the mammary gland to turn red, and ulcers and bleeding may occur.

Loss of Appetite, Weight Loss, and Lethargy

When mammary cancer is confined to the mammary glands, significant symptoms are often not observed. However, if metastasis leads to lesions in the lungs, liver, or other internal organs, loss of appetite, weight loss, and lethargy may appear. If metastasis occurs in the lungs, pleural effusion accumulates, making breathing difficult.
Even if there are no obvious symptoms other than a mammary lump, metastasis may have already occurred. It is important to begin treatment as soon as a lump is noticed.

Treatment for Feline Mammary Cancer

Surgical Removal

For mammary cancer, surgical removal of one or both mammary glands is the first choice of treatment. However, inflammatory mammary carcinoma is a highly malignant type, and surgery is not indicated in such cases.
In the case of feline mammary cancer, even if a lump is found in only one mammary gland, it may have spread to the opposite side. When comparing survival times between bilateral mastectomy and unilateral mastectomy, bilateral is said to be approximately three years, while unilateral is approximately one year.

Chemotherapy

Feline mammary cancer progresses rapidly, and metastasis may have already occurred by the time a lump is noticed. Recurrence or metastasis to organs like the lungs after surgery is common. Therefore, chemotherapy may be used in conjunction with surgery. However, for typical mammary cancer, chemotherapy alone is not usually performed, but it is an option for inflammatory mammary carcinoma.

Difference in Treatment Success Rates with Early Detection

If a lump is discovered at a small stage, metastasis to lymph nodes or other areas may not have occurred. Differences in survival time based on tumor size have been reported: for tumors 2 cm or less, it's over 3 years; for 2-3 cm, 15-24 months; and for over 3 cm, 4-12 months. If discovered when small, life expectancy tends to extend.

Prevention and Daily Care for Feline Mammary Cancer

Timing of Spaying and Preventive Effects

Mammary cancer is related to sex hormones, so the risk of occurrence increases with estrus. Performing a spay before the first estrus reduces the risk by 91%, and performing it before one year of age reduces the risk by 86%. The first estrus for most cats is around 6 months of age, so it is important to spay around that time. The risk of occurrence gradually increases with repeated estrus cycles, so even if the first estrus has occurred, performing surgery as soon as possible will reduce the incidence rate.

Regular Abdominal Checks (Checking for Lumps and Swelling)

Mammary cancer can cause lumps in the abdomen, so regularly feel your cat's belly. If there are lumps near the nipples or a hard area in the abdomen, it could be a mammary tumor.
Even in cats spayed before their first estrus, it can still occur in about 10% of cases, so checking the abdomen is necessary even if your cat has been spayed.

Health Check-ups

Regularly checking your cat's abdomen is crucial for early detection of mammary cancer. However, many cats dislike having their bellies touched. During veterinary health check-ups, a physical examination, which involves palpating the entire body for lumps, is performed. Mammary cancer is more likely to occur in older cats, so aim for a health check-up once every six months.

Summary | Protecting Cats from Feline Mammary Cancer

Most feline mammary tumors are malignant mammary cancers. Mammary cancer progresses rapidly, and it is not uncommon for metastasis to have already begun by the time a lump is noticed. However, if discovered when the lump is small, surgical removal may lead to a cure.
Mammary cancer is hormone-dependent, so spaying reduces the risk of occurrence. Performing surgery before the first estrus makes prevention almost possible.
Regularly check your cat's abdomen for lumps, and if you notice any abnormalities, consult a veterinarian immediately.