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Aromatase Inhibitors in Mammary Tumors

Aromatase Inhibitors in Mammary Tumors

Question

Dear OncoLink "Ask The Experts,"

Can aromatase inhibitors be used to prevent reccurrence of malignant mammary tumors in dogs? If so, which one is indicated, and what dose do we use?

Answer

Lili Duda, VMD, Section Editor of the OncoLink Veterinary Oncology Menu, responds:

We are not aware of any studies published on the effect of aromatase inhibitors in dogs with mammary carcinoma, but based on the fact that many of these tumors are estrogen-dependent, express estrogen receptors, and respond to tamoxifen, it is reasonable to believe that aromatase inhibitors should be effective.

Aromatase inhibitors prevent estrogen synthesis, whereas tamoxifen works by blocking the estrogen receptor. Oophorectomy ("spaying" your dog) ablates the major source of estrogen production. The goal of all of these hormonal therapies is to help prevent mammary carcinoma cells from receiving further stimulation from estrogen.

Unfortunately we cannot provide any information about a specific aromatase drug, its dose, or its effectiveness, since its use is theoretical and no actual canine studies on this have been reported. If the dog is intact, then spaying would be a reasonable, more established approach.