system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
A 62-year-old man comes to the physician because of progressive fatigue and dyspnea on exertion for 3 months. During this time, he has also had increased straining during defecation and a 10-kg (22-lb) weight loss. He has no personal or family history of serious medical illness. Physical examination shows conjunctival pallor. Laboratory studies show microcytic anemia. Test of the stool for occult blood is positive. Colonoscopy shows an exophytic mass in the ascending colon. Pathologic examination of the mass shows a well-differentiated adenocarcinoma. A gain-of-function mutation in which of the following genes is most likely involved in the pathogenesis of this patient's condition?
assistant
KRAS