Breast cancer in dogs

Today is the Susan G. Komen Foundation 3-day walk around here. Hopefully everyone is aware of the cause and has found a way to support the walk for a cure. I thought I would write a piece about breast cancer in dogs. In many ways it parallels the disease in humans. One of the biggest differences is that we have a way to make a MAJOR dent in prevelance of disease. Breast cancer is very difficult to impossible to treat in dogs given our current access to medicines and practical financial limitations. So prevention is the focus!

I can't count the number of times I have an owner look at me in shock when I tell them that one of the main reasons we recommend spaying female puppies is to reduce the risk of breast cancer. Dogs get breast cancer, just like human females. It is also hormonally influenced and patients that have experienced estrogen surges (i.e. heat, estrus, periods) are more likely to develop tumors. There is also a genetic influence. Breast cancer can run in families.

If a female is spayed before her first heat cycle, her risk of breast cancer is less than 5/100ths of a percent. VERY tiny.

If spayed after the first, but before the second, the risk is about 8% (a 160-fold rise!).

If spayed after the second cycle, the risk is just over 26% (about an additional 3-fold rise. these girls are now 520 times more likely to develop cancer).

So that means over 1 in 4 females intact after their second cycle will have breast cancer. That's HUGE. Not to mention the number of females with uterine infections, uterine cancer, and ovarian cancer. Add all ovarian, uterine, and breast tumors together and intact females are about 33% likely to develop cancer of the urogenital system. ONE IN THREE!


Spaying AFTER a second cycle doesn't really lower the odds, however, femals spayed at a mature age are more likely to have benign tumors than females who are intact at the time of tumor diagnosis. Females spayed at any age will have the ovaries and uterus removed, so those girls can't develop ovarian or uterine tumors either.

So make sure you REALLY want those puppies before you give your dog a 1 in 3 chance of developing cancer as opposed to a 1 in 2000 chance if you spay her as a puppy.

Food for thought.


AMH