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Postmenopausal hormones (PMH) have consistently been shown to decrease colorectal cancer (CRC) risk. There is also data suggesting that the presence of Estrogen Receptor (ER-beta1) is positively associated with microsatellite instability (MSI) which may explain the higher incidence of microsatellite unstable tumors in post menopausal women in whom the rebound increase in ER-beta1 expression may occur as estrogen decreases after menopause. We conducted this study to evaluate the effect of PMH use on the association between ER-beta1 protein expression and microsatellite instability(MSI)status in postmenopausal women with CRC. In this population-based study, we used the Surveillance, Epidemiology and End Results (SEER) Program to identify women (50-74 years) with incident CRC from 1998-2002. A 60-minute structured telephone interview was administered to elicit information on hormone therapy (HT) and demographic factors. A sequential sample of 102 cases was examined for ER-beta1 expression by immunocytochemistry (ICC) and tumors with more than 80% positive cells (uniform staining) were considered ER-beta1 positive tumors. Eighty seven cases were evaluated for MSI status using nine standard markers. The Mantel-Haenszel test statistic was used to evaluate whether ER staining varied by postmenopausal estrogen use. We also performed 2 × 2 table statistical analysis using chi-square or two-tailed Fisher’s exact test when appropriate. There was no difference in the proportion (76%) of tumors that were ER-beta1 positive by MSI status (p=0.74). However, among non-users of PMH, a lower proportion (42%) of MSI-H tumors were ER-beta1 positive compared to MSI-SL (79%; p=0.07). In contrast, ever users showed similar proportion of ER-beta1 expression by MSI status (82% vs. 75%; p=0.7). The data suggest that ER-beta1 expression may vary by MSI status among never PMH users but not among ever users.

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA

American Association for Cancer Research
2008