Vikas Sethi, DO1, Adam Jacobs, DO2, Ashwani Sethi, MD, MS3; 1Largo Medical Center, Largo, FL; 2Mount Sinai Medical Center, Miami Beach, FL; 3Lee Health, Fort Myers, FL
Introduction: Prostate adenocarcinoma is one of the most common forms of cancer in men. Common areas of metastasis include bone and lymph nodes. However, several less common sites of invasion exist which require histological confirmation, especially in patients with a history of prostate cancer. Misdiagnosis can lead to inappropriate treatment and complications. We present a rare case of metastatic prostate adenocarcinoma in the rectum discovered during colonoscopy.
Methods: An 85-year-old patient with a history of prostate adenocarcinoma (Gleason 3+3=6) status post brachytherapy, cryosurgery, and intermittent androgen deprivation therapy (ADT) presented with a one year history of altered bowel habits, intermittent rectal pain, and bleeding. CT colonogram showed a low rectal mass with lobulated margins extending into perirectal fat. Colonoscopy revealed a rectal infiltrating mass 4-5 cm from the anal verge. Biopsy and immunohistochemistry confirmed poorly differentiated AE-1/AE-3 and NKX3.1 positive adenocarcinoma of prostatic origin. Axumin PET Scan demonstrated abnormal uptake in the left perirectal and left pelvic lymph nodes. Due to lack of obstructive symptoms, the patient was started on systemic therapy with Enzalutamide 160 mg PO daily with follow up PSA every 2-3 months to monitor progress. Discussion: Rectal metastasis of prostate adenocarcinoma is a rare finding with few cases reported in the literature. This is likely because Denovilliers’ fascia serves as an anatomic barrier between the rectum and the prostate. Literature review suggests several potential routes of dissemination to the rectum including direct invasion of Denovilliers’ fascia, lymphatic dissemination, and seeding of the tissue during needle biopsy. Patients may present with symptoms of bowel obstruction, rectal pain or bleeding, and changes in bowel habits typical of rectal tumors without urological symptoms of prostate tumors.
Immunohistochemical examination is imperative in making a definitive diagnosis. Treatment methods in prior case reports include chemotherapy, radiation, hormone therapy, and surgical intervention with neoadjuvant ADT. It is not clear if rectal metastasis in prostate adenocarcinoma portends a poor prognosis. Collation of data from these rare cases, including our own, may help define the prognosis and appropriate management of such a metastatic tumor.
Disclosures: Vikas Sethi indicated no relevant financial relationships. Adam Jacobs indicated no relevant financial relationships. Ashwani Sethi indicated no relevant financial relationships.