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Case Reports

Abstract

We present a case of a 50-year-old African American male with a history iron deficiency anemia that presented with a 5-year history of a slowly enlarging mass on his left superior cheek. The lesion underwent planned surgical excision, and histopathologic examination of the lesion revealed mucinous carcinoma. Immunohistochemical staining showed that tumor cells were negative for CDX2 and CK20, and largely negative for p63, findings that did not clearly support either a primary cutaneous or metastatic origin. Given the potential for cutaneous metastasis, the patient underwent whole-body positron emission tomography (PET), which demonstrated increased uptake in the colon and anorectal area. He is currently scheduled for a colonoscopy to evaluate for a possible primary gastrointestinal malignancy, particularly given his recent history of iron deficiency anemia and constipation.

Primary and metastatic mucinous carcinoma are difficult to differentiate on histology alone. CK5/6, p63, CK7, and CK20 may be used to differentiate the two. The presence of p63 and CK5/6 positivity favors a primary cutaneous origin, although variability may exist; thus, further workup may include imaging such as CT, MRI, or colonoscopy for rectal lesions, particularly when histologic evaluation is non-confirmatory. Distinction of these two entities is crucial, as five-year survival rates for metastatic mucinous carcinoma are roughly 33%. This case highlights the importance of including imaging and endoscopic studies to exclude internal primary malignancies in patients diagnosed with cutaneous mucinous carcinoma. Early recognition and appropriate staging are critical for guiding treatment and prognosis.