Mammary Tumors in Cats

Ronald M. Bright, DVM, MS, DACVS

BASIC INFORMATION TREATMENT AND FOLLOW UP Description Mammary gland tumors are benign or malignant masses that Treatment Options develop in breast tissue. They are the third most common tumor in Surgery is the most common treatment for mammary tumors in the cat and account for about 17% of all tumors in the female cat. the cat. Older, intact (unspayed) cats are most often affected. Siamese • In most cases, because of the aggressive nature of mammary cats are at twice the risk for developing mammary tumors and tumors in cats, radical surgery is necessary. This may include often develop them at an earlier age. Male cats may rarely develop removal of one or both mammary chains (complete mastec- mammary tumors but usually at an older age than the females. tomy) depending on the location of the tumors. Causes • Because these tumors often invade into deeper structures such Cats can develop mammary tumors secondary to the influence of as the muscle, additional tissues must often be removed. estrogen or progesterone hormones. Intact cats have a seven-fold • Sometimes removal of nearby lymph nodes is also recom- increased chance of developing a mammary tumor if they are not mended at the time of surgery. spayed before 6 months of age. Use of progesterone-like drugs also Removal of the ovaries and uterus is considered part of the treat- increases the chance that a cat will develop a mammary tumor. ment of these tumors, since ovarian and uterine disease often coex- ists with mammary tumors. Spaying of the cat is often delayed until Clinical Signs the mastectomy surgery has healed and the cat has fully recovered. The breasts toward the front of the chest are affected most com- Radiation therapy and chemotherapy have not been very helpful monly. Mammary tumors are usually in an advanced state when (so far) in killing these tumors. they are first noticed, because they have an aggressive nature. They are often attached to underlying structures, and approxi- Follow-up Care mately 25% of the masses are ulcerated on the surface (the skin When a radical mastectomy is done, especially if both sides of the over the mass has raw sores). The nipples are often swollen and mammary chain are removed, the wound is often inflamed and has red and may drain tan or yellow material. In more than 50% of some degree of swelling along the suture line. A soft, padded ban- affected cats, multiple glands are involved. dage is often placed over the surgical site for several days to make Breathing problems related to spread of the cancer to the lungs the cat more comfortable and to protect the wound. Certain post- may be present, and some cats are thin and ungroomed. operative medications may be recommended in these cases. Recheck visits are usually needed after surgery to monitor Diagnostic Tests healing. Periodic laboratory tests and x-rays may be done to moni- The presence of a mass in a mammary gland in an older, intact tor for metastasis if the tumor was malignant. female cat is highly suggestive of a mammary tumor. Fine-needle Prognosis aspiration of the tumor and examination of the cells under the In cats, the size of the malignant tumor is an important prognos- microscope usually confirms the presence of a malignant tumor tic factor. The average survival time after surgery can vary and helps rule out other tumors not arising from mammary tissue. from 4 months to more than 3 years, depending on the size of If a malignant tumor is suspected or confirmed, it is important the tumor. It is important to realize that early diagnosis, combined to determine whether the tumor has spread beyond the borders of with aggressive treatment, provides the best chance for prolonged the mammary tissue. Laboratory tests may be normal but are often survival in cats with malignant mammary tumors. In most cats, recommended prior to biopsy or surgery. X-rays of the lungs and the more radical the surgery (mastectomy involving all mammary an ultrasound may be recommended to check for spread (metasta- tissue compared to regional mastectomy), the better the survival sis) of the tumor. Aspiration of nearby lymph nodes (glands) with times. The success of surgery is often compromised in the cat, a fine needle may also help detect metastasis. however, because of the invasive nature of these tumors.