Prostatic Ductal Adenocarcinoma Masquerading as a Rectal Mass: A Case Report

Abstract

Abstract Objective The approach to a patient presenting with a rectal mass who has a history of bright red blood per rectum (BRBPR) renders a wide range of differential diagnoses. The clinical reasoning to suspect prostatic ductal adenocarcinoma (PDA) in a patient with BRBPR without a classical clinical presentation is highly unlikely. The incidence of PDA is rare with only 0.4% to 0.8% in pure ductal origin. Methods A 71-year-old African American male presented with 3-month history of watery, bloody diarrhea and a recent history of BRBPR with unintentional weight loss. Patient underwent colonoscopy, which showed a large polyp 10 cm from the anal verge, measuring 7 cm. The unclear history of this patient contributed to an initial impression of a colorectal cancer leading to a biopsy of the colonic mass. Results An erroneous diagnosis of tubulovillous adenoma was rendered initially. Further workup showed a large mass originating from the prostate area that was seen penetrating the colorectal region on an abdominal CT scan. The patient’s serum prostate-specific antigen (PSA) level was alarmingly high (4,800 ng/mL) and a subsequent prostate biopsy showed PDA. The colonic biopsy was reviewed again by a genitourinary pathologist and a correct diagnosis was rendered. Conclusion The role of pathology in diagnosing PDA is crucial as patients with PDA can have normal digital rectal examination (DRE) as well as a normal serum PSA level (less than 4.0 ng/mL). Majority of PDAs originate from periurethral prostatic ducts. The unique presentation of primary prostate pathology offers appreciation into the approach and workups to diagnose PDA. Diagnosing PDA can be challenging due to its more aggressive nature of PDA compared to prostatic acinar adenocarcinoma. The clinical reasoning and pathological findings from this rare case can aid clinicians and pathologists to establish the diagnosis of PDA in a timely and efficient manner.