ALDH1A1 and cancer: To fill this gap, we examined the associations of several reproductive factors (parity, age at first birth, breastfeeding, and duration of the time between menarche and first birth) with the expression of well-established stem cell markers CD44 molecule (CD44), CD24 molecule (CD24), and aldehyde dehydrogenase 1 family member A1 (ALDH1A1) in benign breast biopsy samples using prospective data in cancer-free women from the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHSII) and semi-automated computational pathology method for assessment of stem cell marker expression.