Answer the question.

Q. A 41-year-old Caucasian woman presents with fatigue, pallor, weight loss, and intermittent diarrhea. On questioning, she reports a family history of colon carcinoma. Colonoscopy reveals three small polyps in the cecum and a 3-cm ulcerated exophytic mass in the ascending colon. Biopsy is performed and histologic examination of the exophytic mass reveals the tissue shown for your evaluation below. Which of the following is the most likely genetic mechanism of the described pathologic condition?
A) Microsatellite instability due to defective mismatch repair
B) Promoter hypermethylation of tumor suppressor genes
C) Defective nucleotide excision repair with formation of pyrimidine dimers
D) Defective homologous recombination repair due to ATM gene mutation


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