cancer-related genes can be classified into two major groups. proto-oncogenes encode proteins that normally act in promoting cell growth and proliferation. gain-of-function mutations in proto-oncogenes can therefore transform the cells into a cancerous state. tumor suppressor genes, on the other hand, encode proteins that normally function to keep cell proliferation in check. thus, loss-of-function mutations in tumor suppressors can lead to cancer by eliminating the inhibitory effect of these genes. mutations in rtks in cancers are generally termed loss-of-function and thus the rtks are tumor suppressors. true false
