Breast cancer classification to select patients for cancer treatment

Gene expression arrays have shown that breast cancer is comprised of at least four different molecular diseases. These are 1) basal-like breast cancer, 2) human epidermal growth factor receptor 2 (Her2)-positive/estrogen receptor (ER)-negative breast cancer; 3) luminal A breast cancer; and 4) luminal breast B cancer. Basal-like cancer is characterized by ER-negative, progesterone receptor-negative, and Her2-negative expressions. Luminal breast cancer is characterized by ER-positive expression, with the luminal B subtype exhibiting a higher expression of proliferation genes. Several studies have shown that luminal A breast cancer exhibits a better outcome compared with other classes. Also, recent studies have shown that the same subclass is less chemosensitive. These data suggest that some selected luminal A breast cancer cases could be spared adjuvant chemotherapy given their better outcome and lesser chemosensitivity compared with other subtypes of breast cancer. Although other subtypes are more chemosensitive, there is debate about whether some drugs could be active in specific subtypes. Anthracyclines have been reported to be more effective in Her2-overexpressing breast cancer, and cisplatin is currently under investigation in basal-like breast cancer. Finally, some data suggest that luminal B breast cancer exhibits higher sensitivity to aromatase inhibitors. Overall, molecular classes exhibit different sensitivity to conventional drugs. To what extent these data obtained in retrospective biomarker studies could be implemented in daily practice is a matter of debate given the heterogeneity of findings in different studies.