CancerQuest | Feline Mammary Cancer

Feline Mammary Cancer Image

Introduction
Feline mammary cancer (FMC) is the third most common cancer in female cats. It is very uncommon in males, but cases have been reported.⁽¹⁾ The mammary gland tumors that result from FMC can be benign or malignant. However, research shows that 80-96% of mammary tumors are malignant, meaning that they can invade nearby tissues, and are capable of metastasis (spreading to distant parts of the body).⁽¹⁾ ⁽²⁾ Unfortunately malignant mammary tumors tend to be much more harmful.

Cats have four mammary glands on each side of their body, any of which can be affected by FMC. They are referred to as axillary, thoracic, abdominal, and inguinal glands. These glands are the sites of primary tumor growth. As with breast cancer in women, FMC is highly metastatic. As a result, this type of cancer can spread to the lungs, the lining of the lungs and chest cavity (pleura), liver, regional lymph nodes, and other parts of the body.

Genes that have been targeted in human breast cancer research have also been studied in feline mammary cancer. HER-2/neu is the gene that encodes the human epidermal growth factor receptor (type 2) protein. This protein resides on cell surfaces, where it can interact with growth signals. If gene amplification creates extra copies of the HER-2 gene, then its corresponding protein will also be overexpressed. This is thought to lead to increased cell proliferation. HER-2 overexpression has been detected in up to 30% of human breast cancer cases.⁽¹⁾ Similarly, it occurs in 30% of feline mammary cancer cases.⁽³⁾

Risk Factors/Detection/Staging
While all feline breeds may be affected by FMC, some are at a higher risk than others.⁽³⁾ Studies have shown the Siamese breed to have twice the risk of developing this type of cancer.⁽¹⁾ ⁽⁴⁾ Risk increases with age up to 14 years, with an average age of tumor development between 10 and 11 years.⁽¹⁾ ⁽²⁾ Early spaying reduces risk. According to one study, intact females are 7 times more likely to develop mammary tumors than cats that are spayed at a young age.⁽⁵⁾ The latest age at which spaying effectively reduces FMC risk has not been determined.

FMC is most often detected when pet owners or veterinarians feel a mass during examination of the mammary region. However masses can also indicate other conditions, such as severely inflamed lesions, cysts, follicular tumors, and others.⁽³⁾ Histology can be used to confirm the diagnosis and classify the lesion. Tumors are graded as well differentiated, moderately differentiated, or poorly differentiated, based on the appearance of the tissue/cells under a microscope.

Veterinarians and researchers agree that tumor size is the most important prognostic factor in FMC cases, affecting the progression of the disease and the survival time.⁽³⁾ In general, larger tumors have a worse prognosis. Lymph node involvement and degree of metastasis also determine the severity of FMC cases.

Treatment
Surgical removal of mammary tumors is the most common treatment choice. This may include nodulectomy (removal of one or more cell clusters), partial or complete removal of the affected mammary gland(s), removal of lymph nodes, and mastectomy (removal of all glands on the affected side(s)). Veterinarians may use radiation or chemotherapy in addition to surgery. Drugs used to treat FMC include 5-fluoroucil, doxorubicin, cyclophosphamide, methotrexate, prednisone, and vincristine.⁽⁶⁾ It has been shown that cats that respond to doxorubicin-cyclophosphamide treatments survive for longer periods of time.⁽⁶⁾

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References for this page:

Hayes HM, Milne KL and Mandell CP 1981 Epidemiological features of feline mammary carcinoma. Veterinary Record 108 476-479. [PUBMED]
Misdorp W, Romijn A and Hart AA 1991 Feline mammary tumors: a case-control study of hormonal factors. Anticancer Research 11 1793-1797. [PUBMED]
Zappulli V, De Zan G, Cardazzo B, Bargelloni L, Castagnaro M. Feline mammary tumors in comparative oncology. 2005 Journal of Dairy Research 72 98-106. [http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=330933&fulltextType=RA&fileId=S0022029905001263]
Ito T, Kadosawa T, Mochizuki M, Matsunaga A, Nishimura R and Sasaki N 1996 Prognosis of malignant mammary tumors in 53 cats. Journal of Veterinary Medical Science 58 723-726. [PUBMED]
Weijer K and Hart AAM 1983 Prognostic factors in feline mammary carcinoma. Journal of the National Cancer Institute 70 709-716. [PUBMED]
Stolwijk JAM, Minke JMHM, Rutterman GR, Hoekstra J, Prop FJA and Misdorp W 1989 Feline mammary carcinomas as a model of human cancer. II. Comparison of in vivo and in vitro adriamycin sensitivity. Anticancer Research 9 1045-1048. [PUBMED]