Monocyte-to-lymphocyte ratio as a predictive marker for breast cancer treatment outcomes: a narrative review.

Systemic inflammatory markers have gained prominence in cancer research for their prognostic and predictive potential. Among these, the monocyte-to-lymphocyte ratio (MLR) has emerged as a possible indicator of treatment outcomes in breast cancer. This narrative review explores the current evidence regarding MLR as a predictive marker in breast cancer, highlighting its biological rationale, associations with treatment response, and potential clinical relevance. A selective literature search was conducted using PubMed, Scopus, and Web of Science to identify relevant peer-reviewed studies published up to May 2025. Search terms included "monocyte-to-lymphocyte ratio," "MLR," "breast cancer," "prognosis," and "treatment response." Articles were selected based on thematic relevance to breast cancer and MLR. Reference lists of key articles were also screened to identify additional sources. No formal quality appraisal tool was applied, as this review does not follow a systematic review framework. The reviewed studies suggest that elevated pre-treatment MLR is associated with poorer outcomes across various breast cancer subtypes and treatment modalities. However, heterogeneity in study design, MLR cut-offs, and patient populations limits direct comparability. MLR represents a promising, readily accessible biomarker with potential applications in breast cancer prognostication and therapy monitoring. Further prospective studies are required to standardize cut-off values and validate clinical utility.