An unusual delayed rectal metastasis from prostate cancer masquerading as primary rectal cancer

INTRODUCTION AND IMPORTANCE: Rectal metastasis of prostate cancer origin is exceedingly rare. Its clinical presentation, endoscopic morphology, and histopathology are similar to primary rectal cancer. Misdiagnosis may lead to inappropriate treatment. CASE PRESENTATION: We report a case of a gentleman in his 80's with a history of treated prostate cancer T3aN0M0 with radical prostatectomy sixteen years ago. He presented with one-year complaints of altered bowel habits and weight loss. Physical and rectal examination was unremarkable. Colonoscopy manifested some inflammatory changes in the rectum. The pelvis magnetic resonance imaging (MRI) showed an abnormal posterior rectal wall thickening 2 cm above the anal canal. Biopsy confirmed poorly differentiated adenocarcinoma of prostate origin. The staging workup was negative for other distant metastasis. After a multidisciplinary decision, the patient was started on androgen deprivation therapy and given palliative radiotherapy to the rectum. Six weeks later, the patient was stable with mild radiation proctitis. CLINICAL DISCUSSION: Management of rectal metastasis varies depending on the patient's choice, the extent of metastatic burden, symptoms, age, life expectancy, quality of life and comorbidities. While surgery remains the standard of care, other option including radiotherapy, hormonal therapy and chemotherapy has been documented in the literature with survival of few weeks to 2 years. CONCLUSION: Delayed rectal metastasis of prostate cancer after radical prostatectomy is a rare entity. Its clinical presentation and endoscopic and histopathological findings of rectal metastasis are similar to primary colorectal cancer, making diagnosis more demanding.