A method is provided for detecting lymphoid tissues containing shed tumor antigen in an individual. A detector molecule, with binding specificity for shed tumor antigen, is administered to an individual, and detected in the individual is the presence of lymphoid tissue which contains shed tumor antigen, as detected by the signal emitted by the detector molecule bound to shed tumor antigen. The lymphoid tissue, detected as containing shed tumor antigen, may then be surgically removed, thereby removing B cells, shed tumor antigen, and follicular dendritic cells involved in a pro-tumor immune response that are contained in the removed lymphoid tissue.