Tissue samples from the same individual patient

We searched for putative phenotypic and genotypic differences between primary lesions and melanoma metastasis. Therefore we investigated melanoma cells derived either from the primary tumor or from lymph node metastasis of the same individual patient. In vitro studies revealed high migratory and anchorage independent growth of metastasis-derived cells. Unexpectedly, whole genome DNA analysis displayed a total of 10 homozygous losses in the primum-derived cell line, whereas the metastasis–derived cell line only shared 5 of those losses. We further tested these cells in a mouse model for intradermal melanoma growth and detected fast growth of the metastasis-derived cell line and no growth of primum-derived cells. Therefore we suggest that tumor cell progression at the metastatic niche can occur parallel and independently from the primary tumor. Additionally we screened melanoma samples isolated from patients and could identify one case were the primum harboured deletions not present in the metastatic lesion. We propose that for mutation-targeted therapy genotyping should be performed not only from primary, but foremost from metastatic melanoma cells. Blood samples as well tumor samples were directly processed for DNA isolation and subsequent chip hybridization. Each sample was hybridized onto a single affymetrix SNP 6.0 chip.