Miti Saxena

Urban differences in tumor receptor status of breast cancer

BACKGROUND: Data suggest that estrogen and progesterone receptor (ER/PR) status is linked to differential clinical outcomes and breast cancer etiology. Clinically, ER/PR status is used as a decisive factor in treatment recommendations since it can predict the response to therapy, estimate the likelihood and timing of systemic relapse and serve as a marker for survival. On a biological level, because these nuclear receptors are stimulated by levels of circulating estrogen and progesterone, it is reasonable to hypothesize that patients with higher hormonal levels develop ER+/PR+ tumors. Several studies have been done to validate this hypothesis; however, most have been done in industrialized countries with similar social, environmental, and hereditary risk factors. 
The rising incidence rates of breast cancer in parts of the developing world, generally dubbed as low risk environments, warrant similar research. India, for example, has a low incidence of breast cancer in aggregate; however, some urban centers show rapidly increasing rates that rival developed nations. Comparing cases from high incidence areas of India with those from low incidence areas where lifestyle exposures are strikingly different, is a novel way of further validating the existence of sub-types of breast cancer.

OBJECTIVE: To determine whether lifestyle factors and clinical parameters differ between urban versus rural residents of India and whether this translates into distinct sub-types of breast cancer based on ER/PR status.

METHODS: Data for the year 2005 - May 2007 on incident breast cancer cases treated at Tata Memorial Hospital, Mumbai was obtained. Information on estrogen and progesterone receptor status and other important covariates in the etiology of breast cancer was used for the study. Data on clinical parameters were also obtained from the clinical database maintained at TMH. We classified the breast cancer cases into rural, non metro and metro residents as per the 2001 census of India criteria. Unconditional logistic regression was fitted to estimate odds ratios for developing ER+/PR+ tumors compared to ER-/PR- tumors according to residential status (rural vs. urban).

RESULTS: Crude odds ratios of 1.42 (1.13-1.78 CI) and 1.63 (1.28-2.09 CI) were observed for women in non-metro urban and metro urban populations developing ER+/PR+ versus those living in rural areas respectively. Adjusted odds ratios are still to be determined as further analysis is pending.