The pathways and molecules regulating metastasis are of great interest, as tumor spread is the major cause of death in cancer patients. Sentinel- or tumor-draining lymph node (TDLN) pathology analysis currently provide the major diagnostic to assess metastatic potential and the need for adjuvant therapy in many human cancers, including melanoma, colon, breast, and head and neck cancers, suggesting that the lymph nodes are somehow involved in metastasis. We discovered extensive TDLN lymphatic sinus growth and increased lymph flow which precede and predict metastasis in murine models of melanoma, squamous cell carcinoma, and lymphoma. These TDLN alterations could actively promote tumor dissemination via the lymphatics. B cells are required for these TDLN alterations, suggesting the hypothesis that B cells or B cell-derived products drive LN lymphangiogenesis and metastasis. The mechanism of abnormal B cell accumulation in TDLNs will be investigated to determine if it involves abnormal entry, egress, or localization. Potential abnormalities of B cell development or activation will be tested that could promote TDLN lymphatic sinus growth and also result in the incomplete anti-tumor immune response. The contribution of B cell-derived immunoglobulins or other secreted components to TDLN lymphangiogenesis and metastasis will be tested by injection of serum from tumor-nave or tumor-bearing mice into B cell-deficient mice developing melanomas, to determine whether they reconstitute TDLN lymphatic sinus growth and melanoma spread to the TDLN. B cells from different genetic backgrounds will also be transplanted to test the effects of tumor-specific versus no-specific B cells on TDLN alterations and metastasis. Macrophage/myeloid B cell involvement in B cell accumulation and TDLN alterations will be tested, as the innate immune response could promote B cell TDLN accumulation. Molecules induced by tumor-associated innate immune cells could drive B cell accumulation in TDLNs, and these will be screened for by cDNA microarray or immunoassay comparison of tumors, TDLNs, and normal LNs. B cell-derived factors that could drive TDLN lymphangiogenesis will be identified by comparison of TDLN and control LN B cell mRNA and proteins. The contribution of candidate B cell-derived factors to LN lymphangiogenesis and metastasis will then be tested in transplantation assays using B cells that are deficient for lymphatic growth factor expression. These studies will provide insight to the requirements for TDLN B cell accumulation, antitumor antibody response, and lymphangiogenic growth factors in the promotion of TDLN lymphangiogenesis and metastasis. These insights will inform strategies for the development of diagnostic tools and targeted therapies to identify and prevent metastasis in human cancer patients.