KRAS and neoplasm: Tumor heterogeneity has been observed both between patients (interpatient heterogeneity) and within patient tumors (intratumoral heterogeneity).29 Patient tumor sampling and biomarker testing, particularly before enrolment in relevant clinical trials, have demonstrated activating mutations present in proteins such as KRAS,30 BRAF31 and EGFR32 within tumors and between patients.