Presentation Description / Session Abstract: The role of estrogen in canine mammary tumors/human breast cancer has been well established. In both species, the cancer risk is directly correlated with the dose and duration of exposure of breast/mammary tissue to estrogens. The carcinogenic effects are predominantly mediated via the estrogen receptor (ER), and because of this, preventing the interaction between estrogen and receptor has been utilized both for breast cancer prevention (dogs and humans) and breast cancer therapy (humans). The benefit of ovariohysterectomy (OHE) in dogs with mammary tumors has been more controversial, but recent data from veterinary oncology have shown that similar effects may be observed also in dogs with high-risk, ER-positive tumors undergoing OHE, when compared to intact dogs, confirming the similarities to human breast cancer. Interestingly, and contrary to the simplistic view of estrogen as a breast carcinogen, however, the greatest benefit was noted in dogs with high serum estrogen. This was documented both in dogs with ER-positive and ER-negative tumors, suggesting that estrogen may work via ER dependent and ER-independent mechanisms. These finding are corroborated by a decreased risk of other non-mammary cancers in dogs with high serum estrogen, and thus shed light on the epidemiological studies documenting increased risk of various non-mammary tumors in dogs that are spayed at an early age. Further research is needed to further understand these complex and opposing interaction between hormones and cancer, but the dog model and the differences between the estrus cycles in dogs and humans provide a unique opportunity to answer these questions.
Learning Objectives:
Understand the complexity of estrogen in mammary tumors
Understand how to use information regarding estrogen and ER to make good treatment decision (to spay or not to spay)
