NRAS and cancer: However, these signatures are hard to target, and direct links between a single cancer mutation and metastatic tropism to a given organ, such as those suggested by observational studies of NRAS and KRAS mutations in pulmonary and hepatic metastasis of colon cancer and melanoma (Tie et al, 2011; Urosevic et al, 2014; Lan et al, 2015; Pereira et al, 2015; Ulivieri et al, 2015), are intriguing and of potential clinical value.