Letter to the Editor: Comment on "Vitamin D Supplementation Improves Pathological Complete Response in Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy".

We read with great interest the recent randomized controlled trial reporting that vitamin D supplementation significantly improves pathological complete response (pCR) in breast cancer patients undergoing neoadjuvant chemotherapy (NCT). While the findings are noteworthy and contribute to the expanding literature on the supportive role of vitamin D in oncology, several critical methodological issues warrant further discussion. Specifically, the study did not adjust for key clinicopathologic variables-such as tumor subtype, T and N stage, lymphovascular invasion, and treatment intensity-that are well-established predictors of pCR. The lack of multivariate analysis raises concerns regarding potential confounding. Furthermore, the categorization of molecular subtypes lacked granularity, particularly in the distinction between luminal A and B tumors, which are known to exhibit divergent treatment responses. The study's narrow focus on pCR, without reporting other relevant pathological endpoints such as ypT/ypN stage or Miller-Payne grading, also limits its clinical interpretability. Importantly, ethical concerns arise from assigning patients with vitamin D deficiency to placebo, given the growing evidence supporting its correction in oncologic care. Addressing these limitations in future studies could enhance the reliability and translational relevance of the observed findings.