KRAS and colorectal carcinoma: Subsequent pyro-sequencing of DNA from both primary and propagated CB42 as well as 10 other primary colon tumors confirmed the KRAS mutation only in propagated CB42, but found no KRAS mutations in any of the other samples, thus suggesting that activation of KRAS was not required for primary colon tumor initiation in the CRC model, but was required for malignant growth of the tumor during propagation and metastasis.