Prostate Cancer Metastases to the Rectum

Abstract

Prostate cancer (CA) is the 2nd most common CA in men, affecting 1 in 6 males. Prostate CA is well known to metastasize to bones, lymph nodes, lungs, liver, and brain. We present a rare case of metastatic prostate CA diagnosed in a rectal polyp. A 78 year-old male with emphysema, hypertension, diabetes, and prostate CA (Gleason score 8, PSA 11.48ng/nL) treated with radiation, adjuvant leuprolide for 2-years, and transurethral resection of the prostate 8-years prior presented to primary care with early satiety, bloating, and decreased appetite. Review of systems was positive for subjective weight loss and negative for nausea, vomiting, change in bowel function, hematochezia, or melena. There was no family history of malignancy and the patient never smoked. A screening colonoscopy 4-years prior detected a 10mm advanced adenoma without dysplasia and four 4-6mm adenomatous polyps. Given his current presentation, an esophagogram was obtained showing age-related dysmotility, and the patient was referred to gastroenterology for evaluation of his alarm symptoms. EGD showed diffuse mildly erythematous mucosa in the gastric antrum and duodenal bulb. Surveillance colonoscopy revealed a non-obstructing medium sized frond-like villous polyp in the rectum with circumferential spread involving 1/3 of the lumen circumference. Pathology of the rectal polyp revealed a poorly differentiated adenocarcinoma with lymphovascular invasion, and tested positive for prostatic acid phosphatase and PSA stains, both consistent with metastatic prostate adenocarcinoma. Further workup included PSA 3.04ng/nL and negative bone scan and CT abdomen-pelvis for metastases. Patient was subsequently referred to urology and initiated on leuprolide. Several cases of extracolonic CA presenting as colon polyps have been described with the following primary malignancies: breast, ovarian, melanoma, stomach, esophageal, and renal CA. Prostate CA has been known to affect the gastrointestinal (GI) tract by direct tumor invasion of the rectum. However, polypoid prostate CA metastases to the GI tract are rare. Prostate CA metastases to colorectal tissue could occur through pelvic lymphatic drainage or by seeding into peri-rectal or rectal tissue along needle biopsy tracts, however this is extremely rare. This unique finding of metastatic prostate CA in a rectal polyp highlights the importance of considering an extracolonic neoplasm as a source of GI symptoms for patients with a history of other primary CA.