For instance, in the melanoma model, Molhoek and colleagues have suggested that fresh tumor cells and cell lines may have differences in activation of some receptor tyrosine kinases (RTKs) and that the lower levels of activated RTKs in fresh samples may be due to deactivated RTKs in stromal cells that are often part of the specimens analysed during in vitro assays [29]. The gene discussed is NTRK1; the disease is neoplasm.