Kathryn B. Horwitz, PhD
University of Colorado Health Sciences Center, Denver, CO

More than 40,000 American women die of breast cancer each year because their primary tumors metastasize to sites beyond the breast. Among all primary breast cancers, 70-80% contain receptors for women's hormones - estrogen (ER) and/or progesterone (PR) receptors - which classifies them as "hormone dependent." Tumors within the breast metastasize by two routes - to the lymph nodes (LN), especially those under the arms, and from there into the blood and distant organs; or directly into the blood and distant organs. Importantly, regardless of the route, metastatic tumors retain hormone sensitivity. Tumors that spread to LN are more than 80% hormone dependent; tumors that spread directly via blood are 65-70% likely to retain hormone dependence. Therefore breast cancer metastases tend to be hormone dependent. Yet at present nothing is known about whether and how hormones influence the metastasic process itself. The reason for this is that no experimental models exist to study this problem. Using past BCRF funds Dr. Horwitz and her team have developed new models of hormone dependent breast cancer metastasis. These are the first models to reliably allow study of the role of women's hormones in the spread of cancer cells beyond the breast. Their plan this year is to study the role of estrogen and progesterone in breast cancer metastasis to LN and more distant sites, like the brain and bones. They expect this will provide insights into how use of hormones, or hormone inhibitors, can be used slow the spread of cancer out of the breast, or the growth of cancer at those distant sites.