Case Report

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

by Pramath Kakodkar1, Dana Diudea1, Selliah C. Kanthan2, and Rani Kanthan1*,

1Department of Pathology and Laboratory Medicine, Royal University Hospital, 103 Hospital Dr, Saskatoon, SK S7N 0W8, Canada.

2Division of General Surgery, College of Medicine, University of Saskatchewan, Saskatoon, Canada.

*Corresponding author: Rani Kanthan, Department of Pathology and Lab Medicine, Royal University Hospital, 103 Hospital Dr, Saskatoon, SK S7N 0W8, Canada.

Received Date: 08 February2024

Accepted Date: 13 February 2024

Published Date: 15 February 2024

Citation: Kakodkar P, Diudea D, Kanthan SC, Kanthan R (2024) Metastatic Merkel Cell Carcinoma In The Splenic Flexure Of The Colon Mimicking Primary Colonic Carcinoma-A Case Report With Literature Review. Arch Surg Clin Case Rep 7: 219. DOI:10.29011/2689-0526.100219


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.

Keywords: Merkel Cell Carcinoma; Endoscopic Biopsy; Uncommon Mucosal Metastasis


Merkel Cell Carcinoma (MCC) is designated as a highgrade primary cutaneous neuroendocrine carcinoma in the current iteration of the World Health Organization (WHO) classification of Endocrine and Neuroendocrine Tumors [1]. This rare entity was first described by Toker in 1972 as a trabecular carcinoma of the skin [2]. Though, the precise cell of origin of MCC remains contentious in the literature, Merkel cells are favored as the cellular progenitor of MCC as they bear histologic and phenotypic similarities as being the only neuroendocrine cells native to the epidermal stratum basale [3].

MCC has a predilection for occurring in the elderly or immunosuppressed, male patients, and classically presents as a painless, rapidly growing violaceous cutaneous lesion arising on the sun-exposed sites of the head and neck [4, 5]. MCC predominantly presents as a localized cutaneous disease (65%) or with regional lymph node metastases (26%), and in a minority of patients with distant metastases (8%) [4]. The Surveillance, Epidemiology, and End Results (SEER) database showed that the 10-year survival rate for MCC was 71%, 48%, and 20% for localized cutaneous disease, regional lymph node metastases, and distant metastases, respectively [6]. The commonest sites for MCC metastasis include distant lymph nodes (60.1%), distant skin (30.3%), lung (23.4%), brain (18.4%), and bone (15.2%) [7]. Metastatic MCC involving the GI tract is an uncommon event with limited evidence based publications [8].

We present a case of metastatic MCC to the colon that on clinical, radiological, and at colonoscopy was presumed to represent primary colonic carcinoma. The endoscopic biopsy however revealed the presence of an uncommon lesion which with additional immunohistochemistry was accurately recognized as metastatic MCC. A previous history of MCC from a presumed unknown cutaneous primary (MCCUP) was confirmed in a right axillary node dissection three years ago.  A comprehensive literature review is also performed to summarize the clinical and pathological insights into cases with metastatic MCC to the colon. The primary objective of our case report is to increase awareness of such uncommon metastases being diagnosed from endoscopic biopsies for a presumed primary colonic carcinoma. Accurate recognition of these uncommon lesions is vital for the discussion of relevant management options that need to be tailored on an individual basis.

Case Presentation

An 82-year-old gentleman presented to the emergency department with increasing confusion and melena over 5 days. This gentleman had complex comorbidities notable for Heyde syndrome, heart failure with reduced ejection fraction (EF= 39%), multivessel coronary artery disease, severe aortic stenosis, wellcontrolled type 2 diabetes mellitus, and atrial fibrillation managed on apixaban. He endorsed a 20-pounds unintentional weight loss over the past year. Physical examination was otherwise unremarkable. Laboratory tests revealed microcytic anemia and prerenal acute kidney injury, and other biochemical tests were all within normal ranges.

In the emergency department, to correct his hypovolemic and microcytic anemia, resuscitation with crystalloid fluid and blood transfusion with 4 units of packed red blood cell were given. Initial colonoscopy was terminated due to multiple unsuccessful attempts to reach the transverse colon related to significant left-sided diverticulosis and inadequate bowel prep. Computer Tomography (CT) enterography (Figure 1) was performed which showed an apple core-type lesion (5 x 3 cm) at the splenic flexure devoid of active bleeding. Repeat colonoscopy evaluation further characterized this lesion as a circumferential ulcerated large mass at 65 cm with an appearance highly suspicious for colonic cancer. Endoscopic mucosal biopsies were procured for pathological analysis, and the patient was transferred to medical oncology with the preliminary diagnosis of primary colon cancer.


Figure 1: Abdominal CT with triple phase enterography

Histopathological evaluation of the left-sided colon mucosal biopsy revealed fragments of ulcer and colonic mucosa with expansion of the lamina propria with sheets of malignant cells (Figure 2A). The basaloid neoplastic cells show a solid architecture, composed of small cells with elongated nuclei, scant cytoplasm, and increased mitotic figures (Figure 2B). Immunohistochemical (IHC) staining of these neoplastic cells showed them to be strongly positive for pan cytokeratin, (Figure 2C), synaptophysin and

chromogranin (Figure 2D). There was no expression of CK7 while Cytokeratin 20 (CK20) showed the classic dot like positivity of the neoplastic cells in contrast to the strong membrane staining of the adjacent colonic glands as seen in Figure 2E. The noncolonic origin of the neoplastic cells was also supported by no expression of CDX2 with strong internal control staining of the colonic glands as seen in Figure 2F. Additional IHC stains expressed in the neoplastic cells were CD117 and Ber-EP4. There was no expression of CD3, CD 20, CDX2, TTF1, NKX3.1, GATA3 and PAX8 immunostains in the neoplastic cells. The Ki-67 proliferating index was over 90%. The histological appearance and the pattern of IHC staining was consistent with Merkel cell carcinoma. Retrospective medical chart review yielded a pathology report from 3 years ago which showed that the patient had a right axillary lymph node dissection that reported MCC metastatic to the lymph nodes from an Unknown Cutaneous Primary [MCCUP]. He had refused adjuvant radiotherapy at that time. This confirmed the diagnosis of an uncommon mucosal metastatic lesion of Merkel cell carcinoma in these colonic biopsies in contrast to the expected primary colonic carcinoma.