My female dog is five years old and she has had several wetting accidents in her sleep. My veterinarian has prescribed stilbestrol or DES (synthetic estrogen), but I am concerned because she had a malignant mammary tumor removed shortly after I had her spayed. Can this hormone increase the risk of another tumor, and should I give it to her?

Veterinary oncologists recommend against this.

There are few, if any, formal studies that have been done to evaluate the effects of supplemental estrogen (synthetic or natural) in dogs affected with mammary gland cancer. Mammary tumors are one of the most common types of cancer in female dogs. Sex hormones such as estrogen do play a role in the development of mammary cancer in the female dog. This is why it is so important to spay a female dog before her first heat cycle. This almost eliminates her chance of ever developing breast cancer.

Almost half of female dogs with breast cancer are estrogen-receptor positive, and approximately 40 percent are estrogen- and progesterone-receptor positive. When estrogen binds to estrogen receptors on a malignant tumor, cancer growth is promoted. Women with breast cancer are put on drugs that are anti-estrogen, which means that the medication competes with the estrogen for the estrogen receptor sites. This helps block these receptors, preventing the estrogen from binding. Affected women are not allowed to take estrogen supplementation.

Because of this, veterinary oncologists do not recommend estrogen supplementation with drugs such as stilbestrol or DES in dogs affected with breast cancer. There are other medications such as phenylpropanolamine that can be used on a daily basis to help prevent urinary incontinence. Phenylpropanolamine is neither a hormone nor a steroid. It acts to help tighten up the urethral sphincter to prevent urine leaking.

08/07/00