Abstract

A 79-year-old male presented to the dermatology clinic for a 5-week history of a tender lump on the lip and an asymptomatic nodule in the right axillary vault. The patient reported associated fatigue and a 30-pound weight loss in the last 6 months. Physical examination revealed a pearly, pink, indurated plaque with central ulceration located on the right upper cutaneous lip and a firm, mobile, skin-colored, nondraining subcutaneous nodule in the right axillary vault. A shave biopsy of the lip revealed a diffuse cellular infiltrate filling the superficial and deep dermis. Morphologically, the cells had abundant clear cytoplasm with eccentrically located, pleomorphic, and hyperchromatic nuclei, with occasional prominent nucleoli. The cells stained positive for AE1/AE3 on immunohistochemistry. A punch biopsy of the nodule in the right axillary vault revealed a morphologically similar proliferation of cells. The patient subsequently underwent colonoscopy, which revealed a completely obstructing, circumferential mass in the distal ascending colon. A biopsy of the mass confirmed invasive adenocarcinoma, supporting a diagnosis of cutaneous metastases from adenocarcinoma of the colon. Signet ring cell adenocarcinomas (SRCCs) are characterized by a proliferation of neoplastic cells, which resemble signet rings due to the accumulation of intracytoplasmic mucin and subsequent displacement of the nucleus to the cellular periphery. The neoplastic cells stain positive for mucicarmine due to the abundant intracytoplasmic mucin. SRCCs comprise 1% of all colon adenocarcinomas and cutaneous metastasis from SRCC of the colon is rare. Uncommonly, cutaneous metastasis of colorectal SRCC precedes the diagnosis of the primary lesion. We present this case because of the unusual signet ring morphology of cutaneous metastasis, which extraordinarily heralded the diagnosis of primary adenocarcinoma of the colon.

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