S1725 Case Report: Prostate Cancer Diagnosed on Rectosigmoid Biopsies in a Patient Presenting With Diarrhea

Abstract

INTRODUCTION: Prostate cancer is the second most commonly diagnosed cancer in men worldwide. Despite the anatomic proximity, rectosigmoid involvement of prostate adenocarcinoma is rare. We present a case of metastatic prostate cancer diagnosed on rectosigmoid biopsies in a patient presenting with diarrhea and fecal urgency. CASE DESCRIPTION/METHODS: A 76-year-old male presented to clinic for evaluation of non-bloody diarrhea with associated fecal urgency. His medical history was significant for prostate adenocarcinoma diagnosed and treated nine years ago with prostatectomy, radiation, and androgen deprivation therapy (ADT). On current presentation, labs showed a normal complete blood cell count, TSH, and tissue transglutaminase IgA. Stool studies were negative for gastrointestinal pathogens. A colonoscopy was performed which demonstrated a normal terminal ileum, sigmoid diverticulosis, and mild radiation proctitis. Random colon biopsies showed changes consistent with collagenous colitis. Treatment for collagenous colitis was initiated, however, three months later the patient continued to have diarrhea as well as new onset abdominal pain, nausea, vomiting, and weight loss. Imaging showed sigmoid colon wall thickening, an ill-defined soft tissue mass in the pelvis, and lymphadenopathy. Flexible sigmoidoscopy revealed congested and erythematous mucosa beginning at 10cm from the anal verge with multiple clean based ulcerations. Targeted biopsies revealed a population of keratin positive cells with limited differentiation and positive PSA staining consistent with poorly differentiated adenocarcinoma of prostate origin, likely from lymphangitic spread. The patient was diagnosed with metastatic castrate-resistant prostate adenocarcinoma and started on ADT. DISCUSSION: Rectosigmoid involvement by prostate adenocarcinoma is rare and review of available literature suggests at least three potential routes of involvement including direct invasion through Denonvilliers’ fascia, lymphatic metastasis, and implantation after transrectal biopsy. Rectosigmoid involvement of prostate adenocarcinoma may present with symptoms including change in bowel habits, rectal urgency, lower gastrointestinal bleeding, and pelvic pain. The case presented here emphasizes the importance of including prostate adenocarcinoma on the differential diagnosis in men presenting with lower gastrointestinal symptoms and abnormal rectosigmoid mucosa on colonoscopy, especially in patients older than 65 years or with a history of prostate adenocarcinoma.Figure 1.: Congested and erythematous mucosa starting approximately 10 cm from the anal verge.Figure 2.: Rectosigmoid ulcerations with surrounding erythematous mucosa.Figure 3.: Ill-defined soft tissue mass in the peri-rectal region with lymphadenopathy.