Colorectal Carcinoma

A 58-year-old man presents with a 3-month history of altered bowel habits and blood in stools. Digital rectal examination reveals a palpable mass 7 cm from the anal verge. Which investigation is most appropriate to confirm the diagnosis and assess local invasion?

Which genetic alteration is the initiating event in the adenoma-carcinoma sequence of colorectal cancer?

Which histological type of colorectal carcinoma has the worst prognosis and is associated with microsatellite instability and mismatch repair deficiency?

A 58-year-old man from Delhi presents with a 3-month history of altered bowel habits, blood-stained stools, and weight loss of 4 kg. Digital rectal examination reveals a hard, irregular mass 6 cm from the anal verge. Colonoscopy confirms a left-sided colonic mass with biopsy showing moderately differentiated adenocarcinoma. CT abdomen/pelvis shows no distant metastases. What is the most appropriate next step in management?

A 62-year-old woman from Delhi undergoes colonoscopy for iron-deficiency anaemia and is found to have a 3 cm polypoid lesion in the caecum. Histopathology shows invasive adenocarcinoma arising from a tubulo-villous adenoma with high-grade dysplasia. The tumour invades into the submucosa but does not breach the muscularis propria. Immunohistochemistry shows loss of MLH1 and PMS2 expression. Which molecular pathway is most likely implicated in the pathogenesis of this tumour?