Parity and Lactation in Relation to Estrogen Receptor Negative Breast Cancer in African American Women

Abstract

Background Estrogen receptor (ER) negative, progesterone receptor (PR) negative breast tumors occur more commonly in women of African ancestry. Recent research indicates that the effects of reproductive factors may differ by hormone receptor status. We assessed the relation of parity and lactation to incidence of ER−/PR− and ER+/PR+ breast cancer in a cohort of African American women. Methods From 1995–2009, 457 incident cases of ER+/PR+ and 318 cases of ER−/PR− breast cancer were confirmed by review of pathology data among 59,000 African American women followed in the Black Women’s Health Study through biennial questionnaires. Hazard ratios (HR) and two-sided 95% confidence intervals (CI) for the incidence of breast cancer subtypes were derived from proportional hazards regression models that controlled for age, reproductive variables, and breast cancer risk factors. Results Higher parity was associated with an increased risk of ER−/PR− breast cancer (HR = 1.48, 95% CI 0.98–1.84 for 3+ versus 0 births, p trend = 0.009), and with a reduced risk of ER+/PR+ cancer (HR = 0.53, 95% CI 0.39–0.73 for 3+ versus 0 births, p trend = 0.0002). Among women who had breastfed, high parity was no longer associated with increased incidence of ER−/PR− breast, but the inverse association with ER+/PR+ cancer persisted. Conclusions The higher incidence of ER−/PR− breast cancer in African American women may be explained in part by their higher parity and lower prevalence of breastfeeding relative to white women. Impact Increased breastfeeding may lead to a reduction in the incidence of this breast cancer subtype.

Cultural and Environmental Factors of Triple-Negative Breast Carcinomas

“…In another large study of African American women, breastfeeding was found to be a protective factor against hormone receptor-negative phenotypes [37]. Again, breastfeeding was less common among African American women than other ethnicities [37]. This low rate of breast feeding may indicate a cultural distinction between African American populations and populations of other heritage in the United States.…”

“…An inverse association has been found for length of duration of breastfeeding and risk for developing triple-negative breast cancer [11,12,15,[37][38][39]. In several studies, this reduced risk was found among women who breastfed for a duration of greater than four months [11,12].…”

“…However, possible associations may have been masked by the fact that only 31% of parous African American women in the study breastfed [38]. In another large study of African American women, breastfeeding was found to be a protective factor against hormone receptor-negative phenotypes [37]. Again, breastfeeding was less common among African American women than other ethnicities [37].…”

“…Several studies have found that increased parity is associated with increased risk for a triple-negative phenotype [11,[36][37][38], with one finding that being nulliparous decreased risk 39% [36]. Another study found that in African American women specifically, higher parity increased risk for hormone receptor-negative phenotypes [37].…”

“…However, additional studies have found no association between parity and risk [15], and one study specifically found no association in African American women [38]. Of note, African American women typically have relatively high parity compared with white Americans [11,37,38].…”