Folate Metabolism: A Master Regulator of Lipid-Associated Macrophage Function in Cancer

Cancer progression is shaped not only by genetic alterations but also by systemic and local metabolic changes that influence the tumor microenvironment (TME). In particular, dysregulated lipid metabolism and micronutrient availability can modulate immune cell function and favor the accumulation of immunosuppressive myeloid populations associated with tumor growth, immune evasion, and poor clinical outcome.

Among tumor-infiltrating myeloid cells, macrophages show high metabolic plasticity and adapt their phenotype in response to environmental cues. A subset of macrophages characterized by intracellular lipid accumulation and expression of lipid metabolism-related genes, known as lipid-associated macrophages (LAMs), has been identified in metabolic disorders and, more recently, in several solid tumors, including breast, prostate, and head and neck cancers. In cancer, LAMs are generally associated with immunosuppressive functions, impaired anti-tumor immunity, extracellular matrix remodeling, tumor cell survival, and unfavorable prognosis. Their accumulation may reflect both local metabolic alterations within the TME and systemic metabolic dysregulation, such as obesity and altered lipid homeostasis. However, the factors regulating LAM differentiation and function in human cancers remain poorly defined.

Folate is an essential micronutrient involved in DNA synthesis, repair, methylation, and cellular metabolism. Folate deficiency is frequently observed in metabolic disorders, including obesity, and has also been reported in patients with advanced malignancies. Although epidemiological studies have linked folate status to cancer risk, progression, and mortality, results vary across tumor types and populations. Emerging evidence suggests that folate availability may influence lipid metabolism and immune cell differentiation, potentially affecting macrophage polarization within tumors. Experimental studies indicate that folate depletion can alter fatty acid metabolism and promote lipid accumulation in different cell types. Moreover, folate uptake by macrophages is polarization-dependent, and folate receptor beta is selectively expressed by M2-like, immunosuppressive tumor-associated macrophages, supporting a possible link between folate metabolism and macrophage phenotype.

Altered folate metabolism may therefore contribute to macrophage metabolic reprogramming toward lipid-associated and immunosuppressive states in the TME. Since diet and micronutrient availability are increasingly recognized as modulators of anti-cancer immune responses, understanding the relationship between folate status, lipid metabolism, and LAMs in cancer patients may provide relevant mechanistic and prognostic insights. Given the limited human data available, an observational study using biological samples collected during routine clinical care represents an appropriate approach to investigate these associations without exposing participants to additional risks.