A model system to quantitate tumor burden in locoregional lymph nodes during cancer spread

In order to quantitate the metastatic burden of secondary tumor deposits in locoregional lymph nodes, we produced a green fluorescent protein (GFP)-expressing murine cell line (B16F1) metastatic to lymph nodes in immunocompetent mice. When implanted into the hindleg of mice, all animals developed paraaortic lymph node metastases. Fluorescence microscopy, immunohistochemistry, and RT-PCR confirmed the presence of metastatic cells in lymph nodes. Tumoral deposits occurred preferentially in marginal sinuses and spread superficially to the subcortical area. Western blot analysis showed that the local tumor burden could be quantitated in individual lymph nodes. This model system should be useful for quantitating metastatic invasion particularly of micrometastases and aid in the development of lymphotropic drugs to detect and/or treat lymph node metastases in advanced cancers.