To study the association between the cortical thickness of axillary lymph nodes (exposure) and the humoral response quantified by PVST (outcome), we defined lymph nodes showing a cortical thickness greater than 3 mm as morphologically reactive lymphadenopathy, and a total antibody (IgG+IgM) quantification equal or greater than 1000 U/mL as a protective serologic level. The gene discussed is CD40LG; the disease is Lymphadenopathy.