CD40LG and melanoma: Toward elucidating these disparate host-protective vs. tumor-promoting functions, the current study aimed to evaluate associations between pre-diagnostic serum markers of the humoral immune system, immunoglobulin G (IgG), IgA and IgM, and risk of melanoma in the prospective Swedish Apolipoprotein-related MORtality RISk (AMORIS) cohort study.