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Spaying your dog before her first heat cycle can dramatically reduce her risk of breast cancer.

Charlotte recovers after being spayed at Cal West.

Mammary cancer is the most common neoplasm in intact female dogs. Dogs spayed before their first estrous (heat) cycle have a greatly reduced risk of developing breast cancer, with the risks rising to 26% of dogs that are spayed after their second estrous. Breast cancer primarily affects late middle-aged (9-11 years) female intact dogs with an increased incidence beginning at approximately 6 years of age.


Dogs spayed prior to their first estrus have a 0.5% risk of developing mammary tumors in their lifetime. The protective effect being spayed decreases quickly over the first few estrus cycles, and most studies have not found a significant benefit after 4 years of age. Other risk factors for breast cancer include obesity and a diet high in red meat.


Withrow and MacEwan’s Small Animal Clinical Oncology 5th edition. Withrow, Vail, Page (Ch. 27)

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