As the mode of cell death involved in the tumor response to metronomic chemotherapy with endocrine therapy (chemoendocrine therapy) remains to be elucidated, we studied autophagy-related markers, beclin 1 and LC3, and apoptosis-related markers, TUNEL and M30, in archived breast cancer tissue specimens from a prospective multicenter neoadjuvant chemoendocrine trial, JBCRG-07, in which an oral cyclophosphamide was administered together with an aromatase inhibitor, letrozole, in postmenopausal patients with HR-positive breast cancer. This evidence concerns the gene CYP19A1 and breast cancer.