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Abstract

We present a case of a 49-year-old man referred to dermatology for presumed “dermoid cyst” removal. Examination revealed multiple 1–3 cm, flesh-colored, firm nodules on the scalp, chest, and back, which were painless and slowly enlarging over two months. Punch biopsy showed dermal and subcutaneous infiltration by malignant glands and single cells with signet ring-like features. Tumor cells were positive for CKAE1/AE3, CK20, CDX2, and negative for CK7. Review of the patient’s history revealed goblet cell adenocarcinoma of the appendix, grade 2, pT3N0M0, diagnosed six years earlier and treated with right hemicolectomy and partial FOLFOX chemotherapy. Three months prior to dermatology referral, he developed urinary symptoms and a bladder mass was found on imaging. Transurethral resection revealed adenocarcinoma with signet ring-like features, positive for CK20, CDX2, β-catenin, and negative for CK7. Molecular testing revealed KRAS p.G12V and low tumor mutational burden—findings supporting a carcinoma of lower gastrointestinal origin. Two months prior to dermatology referral, bilateral pleural effusions showed malignant signet ring-like cells on cytology, CK20+, CDX2+, and CK7–. This case highlights the importance of biopsy in evaluating new skin nodules in patients with a cancer history—even when the primary tumor type rarely metastasizes to skin. Histologically, this case raises the differential diagnosis of cytokeratin-positive signet ring-like cells in the skin. In addition to metastatic adenocarcinoma, other considerations include adnexal carcinomas with mucinous or clear cell change, Paget disease, melanoma with signet ring-like features and epithelioid sarcoma. Accurate classification requires integration of clinical, histologic, immunohistochemical, and molecular data.