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- For mammary tumors in humans, please see breast cancer.
Mammary tumors in dogs
Biology
Female dogs who are not spayed or who are spayed later than the first heat cycle are more likely to develop mammary tumors. Specifically, dogs not spayed or spayed after the age of two years are seven times more likely to develop mammary tumors than dogs spayed by six months old. The tumors are often multiple. They are most commonly seen between the ages of eight and ten years old.About 50 percent of mammary tumors in dogs are malignant. Adenomas and fibroadenomas make up the benign types. Malignant mammary tumors are divided into sarcomas, carcinosarcomas, inflammatory carcinomas (usually anaplastic carcinomas), and carcinomas (including adenocarcinomas), which are the most common. Inflammatory carcinomas describe tumors that are fast growing and have bruising, edema, and pain. They can cause disseminated intravascular coagulation.
Malignant tumors are also subdivided histopathologically into those showing blood vessel wall invasion and those that do not. Without blood vessel wall invasion there is a better prognosis. Dogs with noninvasive adenocarcinomas have an average survival time of two years, while dogs with invasive adenocarcinomas have an average survival time of one year. Tumor size also affects the prognosis, in that dogs with smaller tumors have longer survival times. Tumor type is also important. Sarcomas and carcinosarcomas carry an average survival time of nine to twelve months. Inflammatory carcinomas have a very poor prognosis, and have usually metastasized by the time of diagnosis. Metastasis for any malignant mammary tumor is usually to the regional lymph nodes and lungs.
Diagnosis and treatment
Appearance and location of the tumor is enough to identify it as a mammary tumor. Biopsy will give type and invasiveness of the tumor. Surgical removal is the treatment of choice, but chest x-rays should be taken first to rule out metastasis. Removal should be with wide margins to prevent recurrence, taking the whole mammary gland if necessary. No study has shown that spaying at the time of tumor removal helps to prevent recurrence or to improve survival times, but since 40 to 50 percent of dog mammary tumors have estrogen receptors, it is still recommended by many veterinarians. Chemotherapy is rarely used.Breeds at increased risk
Mammary tumors in cats
Intact cats are seven times more likely to develop mammary tumors than cats spayed between the ages of six and twelve months. Siamese cats seem to have increased risk. Malignant tumors make up 90 percent of mammary tumors in cats, almost all adenocarcinomas. Like in dogs, tumor size is an important prognostic factor. One study showed that tumors less than two centimeters (cms) in diameter carry an average survival time of 4.5 years. Tumors two to three cms carry an average survival time of two years and tumors greater three cms carry an average survival time of six months. About 10 percent of cat mammary tumors have estrogen receptors, so spaying at the time of surgery has little effect on recurrence or survival time. Diagnosis and treatment is similar to the dog. There is a better prognosis with radical surgery (removing the whole mammary chain) than with more conservative surgery.
Mammary tumors in other animals
Mammary tumors in ferrets
Mammary tumors are rare in ferrets. Appearance tends to be a soft, dark colored lump. Most seem to be benign and occur most frequently in neutered males. Surgery is recommended.Mammary tumors in guinea pigs
Mammary tumors in guinea pigs occur in males and females. Most are benign, but 30 percent are adenocarcinomas. They usually do not metastasize, but aggressive surgery is necessary to prevent recurrence.Mammary tumors in mice
Most mammary tumors in mice are adenocarcinomas. They can be caused by viral infection. Recurrence rates are high, and therefore there is a poor prognosis.Mammary tumors in rats
Most mammary tumors in rats are benign fibroadenomas. Less than 10 percent are adenocarcinomas. They occur in male and female rats. The tumors can be large and occur anywhere on the trunk. There is a good prognosis with surgery. Spayed rats have a decreased risk of developing mammary tumors.Mammary tumors in hamsters and gerbils
Mammary tumors tend to be benign in hamsters and malignant in gerbils.References
"Mammary tumor"