Stout NK, et al. - Researchers investigated if contralateral breast cancer (CBC) risk in women (aged 40-79) with ductal carcinoma in situ (DCIS) can be affected by estrogen-receptor (ER) status. They used the Surveillance, Epidemiology, and End Results database to select cases diagnosed between 1990 and 2002. They also determined what factors predicted time from index DCIS to CBC (invasive or in situ) via multivariable competing risk regression. A highly significant predictor of CBC was found in ER status. The estimated 10-year cumulative incidence was 5.3% among ER positive (ER+) cases and 3.3% among ER negative (ER−). Overall, irrespective of laterality, ER+ DCIS could be a field effect that confers increased inclination for developing cancer across breast tissue. Conversely, ER− DCIS could be a local isolated event. Treatment and surveillance tactics could be impacted by considering ER status, since most DCIS is ER+, and only a minority of DCIS patients undertake hormonal therapy.