Metastatic Merkel Cell Carcinoma In The Splenic Flexure Of The Colon Mimicking Primary Colonic Carcinoma-A Case Report With Literature Review

Background: Merkel Cell Carcinoma (MCC) is an unusual neuroendocrine neoplasm that usually presents as a primary malignant skin tumor with localized disease. Distant metastasis is uncommon with metastases to the colon being extremely rare. In this case report, we discuss MCC metastasis to the colonic splenic flexure that mimicked primary colon carcinoma. A literature review is also undertaken. Case presentation: An 82-year-old man presented with melena and microcytic anemia accompanied by moderate weight loss. Upon investigation, a computer tomography of the abdomen showed a 5 x 3 cm apple core-type lesion at the splenic flexure. Colonoscopy revealed a circumferential ulcerated large mass in the splenic flexure which was biopsied for pathological conformation of presumed colonic carcinoma. Detailed histopathological evaluation of the endoscopic mucosal biopsies with additional immunostaining confirmed the diagnosis of metastatic MCC. Review of his medical records confirmed MCC in the right axillary lymph nodal dissection 3 years ago from an unknown cutaneous primary. Due to accompanying medical comorbidities palliative supportive management was opted. He died a month later from pneumonia and decompensated cardiac failure. Conclusion: MCC metastasis to the colon is an extremely uncommon event. Clinically and radiologically it often mimics a primary colonic carcinoma. Histopathological diagnosis from endoscopic mucosal biopsies by light microscopy alone remains a challenge. Additional immunohistochemical stains are essential for accurate diagnosis. The presence of colonic metastases probably indicates widespread disease as most cases like ours are associated with an extremely high mortality rate. Earlier diagnosis with interventional multimodality treatment options may alleviate this dismal prognosis.