Gastroenterology clinical image challenge: A 68-year-old man with type 2 diabetes presented to the emergency department with acute urinary retention, which was relieved by urethral catheterization. Before this episode, he had progressive urinary frequency and slow urinary stream for three months. He reported no abdominal pain, weight loss, bloody stool or bowel habit change.
On examination, he was afebrile. His abdomen was supple and without tenderness. Digital rectal examination confirmed a firm, irregular tumor in the anterior rectal wall. Laboratory test results including white blood cell count (9030/μL), hemoglobin level (14.2 g/dL) were normal, and normal results were obtained for the routine urinalysis. His serum carcinoembryonic antigen level was 1.7 ng/mL and prostate-specific antigen level was 6.0 ng/mL. Subsequent sigmoidoscopy showed an irregular bulging submucosal tumor with friable, erythematous overlying rectal epithelium. A whole-body computed tomography scan revealed a locally advanced rectal tumor (figure) with diffuse lymphadenopathy around the mesorectum, aorta, mediastinum and neck. Pelvic magnetic resonance imaging also revealed a low signal rectal tumor with regional lymphadenopathy on T2-weighted images.
What is the diagnosis?
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