Ficolin (FCN) 3 is a soluble pattern recognition molecule in the lectin complement pathway, primarily expressed in the liver and lung. Existing studies indicate that FCN3 is generally downregulated in lung adenocarcinoma and squamous cell carcinoma tissues, though its prognostic significance depends on histological subtypes and analytical levels. This review summarizes the expression heterogeneity of FCN3 in lung cancer and its relationship with the immune microenvironment. At present, FCN3 can be considered a candidate stratification marker linking the lectin complement pathway, tissue composition, and immune microenvironment, but its cellular origin, measurement level, and incremental clinical value require further clarification.