To determine whether mutual exclusivity between oncogenic alleles is limited to KRAS and EGFR in lung adenocarcinoma or whether it is a more general phenomenon affecting other cancer lineages, we examined sequencing data from other cancer types with the methodology employed in Figure 1, seeking pairs of mutant proto-oncogenes that are disfavored or incompatible with tumorigenesis. The gene discussed is KRAS; the disease is cancer.