Arena V, et al. - Data on the expression of estrogen receptors, progesterone receptors, and human epidermal growth factor receptor-2 was combined to obtain 8 tumor patterns categorized as triple-negative, nonluminal (i.e. positive for human epidermal growth factor receptor-2 with four subtypes) and luminal (negative for human epidermal growth factor receptor-2 and positive for estrogen receptor and/or progesterone receptor with three subtypes) tumors. In this work, researchers analyzed the proliferative activity of the eight tumor subgroups to ascertain if a high proliferative activity is shown by the ER−/PR+ type compared to the other subtypes, that correlate it to more the aggressive behavior. Estrogen receptor, progesterone receptor, human epidermal growth factor receptor-2 and Ki67 data from 6643 cases of breast cancer indicated consistently much higher proliferative activity in the tumor type that were positive for only the progesterone receptor and negative for both the estrogen receptor and human epidermal growth factor receptor-2 (1.3% of all cases) compared to those of the other luminal subtypes