A 62-year-old woman from Delhi presents with a 4-month history of progressive abdominal distension, early satiety, and weight loss of 8 kg. On examination, she has ascites and a firm, fixed mass palpable in the right lower abdomen. CT abdomen shows a caecal mass with peritoneal nodules and ascites. Colonoscopy reveals a fungating lesion in the caecum; biopsy confirms adenocarcinoma. Serum CEA is elevated at 12 ng/mL. Which of the following molecular alterations is most commonly associated with right-sided colorectal carcinomas like this one?