Breast cancer and mammary tumors in pets

Breast cancer and mammary tumors are common in pets. Yes, dogs, cats and small mammals may contract the dreaded disease as well as humans. A non or late spayed female dog has twice to three times the chance (25%) of getting breast cancer then a woman. Overall, 50% of tumors in female dogs are breast tumors. 

Breast tumors can be malignant (cancer) or benign. Malignant tumors spread all over the body and destroy vital tissues and organs like lungs, liver, bones and more. Benign tumors, on the other hand, grow locally and damage the adjacent tissues. Fifty-percent of breast tumors in dogs and 85-90% in cats are malignant. Half of the malignant tumors and a large portion of the benign tumors are stimulated by the female sex hormones and therefore tend to be more aggressive on intact females. Dogs and cats usually have eight to ten pairs of glands along the abdomen. Most tumors occur in middle aged females and involve the rare two sets of glands. Mammary tumors in cats are more common in old females and involve the front two pairs of glands. 

Early detection is very important. Pet owners should always be on the lookout for nodules, lumps or change in the consistency of the mammary gland. Normal glands are soft and elastic. Any nodule or swelling should be checked by the veterinarian as soon as possible. Chest x-rays and blood tests are recommended preliminary procedures, as treatment might be pointless in case of advanced tumor cells spreading and tissue damage. Once the preliminary tests are negative, suspected tumors are removed or biopsied. The tissue sample is sent to the laboratory for diagnosis. Life expectancy may increase if a hysterectomy (spay) is done as well. Frequent follow-up exams and periodic chest x-rays are needed to detect possible recurrences. Chemotherapy and radiation treatment are of limited value. 

Post-surgical survival time may range between several weeks to several years, depending on the severity of the tumor. Large, fast-growing ulcerated and deep tumors carry worse prognosis. Evidence of spreading to the lungs (done by x-rays) or lymph nods (done by needle aspirate or a biopsy) also indicates advanced stage of the malignancy. 

Early spaying (before the first heat cycle) reduces the risk of mammary tumors to 0.5%. If done after one period, the risk can be reduced to 8% of that in intact female dogs. Spaying at maturity is much less effective in preventing breast cancer.

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Yuval Nir
Naperville University Commons Animal Clinic-
1827 Wehrli rd
Naperville , IL , 60565
(630) 544-3333
Veterinarians, Animal hospital