Spontaneous regional lymph node metastases of three variants of the B16 melanoma: Relationship to primary tumor size and pulmonary metastas

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Abstract
We studied the patterns of spontaneous regional lymph node metastases of three variants (Fl, F10, and BL6) of the B16 melanoma in C57BL/6 mice and related the incidence to primary tumor size and pulmonary metastases. The incidence of regional lymph node and pulmonary metastases correlated with increasing primary tumor size (p ⩽ 0.0001). The incidence of pulmonary metastases in mice whose regional lymph nodes did not contain tumor also correlated with increasing primary tumor size (p ⩽ 0.0001). This propensity for direct hematogenous spread was more apparent in BL6 tumors than in F1 and F10 tumors (p ⩽ 0.0001). BL6 tumors also metastasized to regional nodes at smaller primary tumor sizes (p ⩽ 0.04). Heterogeneous variants that metastasize earlier to regional lymphatic and hematogenous sites dictates the natural history of the primary tumor. Whether prophylactic lymphadenectomy for melanomas is therapeutic may depend on dissemination-related phenotypic characteristics.