Estrogen receptor (ER) status is an important biomarker in defining subtypes of breast cancer differing in antihormonal therapy response, risk factors and prognosis. However, little is known about association of ER status with various risk factors in the developing world. Our case-control study done in Kerala, India looked at the associations of ER status and risk factors of breast cancer. From 2002 to 2005, 1,208 cases and controls were selected at the Regional Cancer Center (RCC), Trivandrum, Kerala, India. Information was collected using a standardized questionnaire, and 3-way analyses compared ER1/ER2 cases, ER1 cases/controls and ER2 cases/controls using unconditional logistic regression to calculate odds ratios and 95% confidence intervals. The proportion of ER2 cases was higher (64.1%) than ER1 cases. Muslim women were more likely to have ER2 breast cancer compared to Hindus (OR 5 1.48, 95% CI 5 1.09, 2.02), an effect limited to premenopausal group (OR 5 1.87, 95% CI 5 1.26, 2.77). Women with higher socioeconomic status were more likely to have ER1 breast cancer (OR 5 1.48, 95% CI 5 1.11, 1.98). Increasing BMI increased likelihood of ER2 breast cancer in premenopausal women (p for trend < 0.001). Increasing age of marriage was positively associated with both ER1 and ER2 breast cancer. Increased breastfeeding and physical activity were in general protective for both ER1 and ER2 breast cancer. The findings of our study are significant in further understanding the relationship of ER status and risk factors of breast cancer in the context of the Indian subcontinent. '
UICCKey words: estrogen receptor; breast cancer; India Estrogen receptor (ER) status of breast tumors has been instrumental in defining an important subtype of breast cancer with differences observed in risk factors, treatment and prognosis. [1][2][3][4][5][6][7] Numerous studies in the past have looked at differences in etiology and risk factors pertaining to presence or absence of ER-alpha. Most of these studies were conducted in Western populations as early as 1980s. [1][2][3][4][5] Around the same time, it was also discovered that ER1 tumors that lacked progesterone receptor (PR) expression were less responsive to endocrine therapy compared to tumors that expressed PR. 8 This led to studies in the past decade that looked at the link of various risk factors of breast cancer and combined ER/PR information to better explain the underlying differences between the various subtypes of breast cancer. 9-13 Chen and Colditz 14 have emphasized the importance of taking into account the ER/PR status information of breast tumors both for effective treatment as well as risk prediction for instituting prophylactic measures. Although there might be numerous ways to subtype breast cancer, the classification into ER1 and ER2 cancer remains a key divider. 14 However, information related to ER status is lacking for populations in developing countries. In fact, in most developing countries, determination of hormone receptor status is not a part of standard pro...