Abstract

Lung adenocarcinoma is one of the most common malignancies in the United States and has a relatively high mortality rate. Cutaneous metastasis is rare and is seen primarily in the context of widely metastatic disease. Our patient is a 69-year-old female with history of tobacco smoking and biopsy-proven stage IV lung adenocarcinoma on immunotherapy. A few months into treatment, she presented with a new slowly growing 1.0 cm pink plaque on her right parietal scalp with plugged hair follicles. The clinical differential diagnosis included seborrheic keratosis, squamous cell carcinoma, basal cell carcinoma, amelanotic melanoma, and a biopsy was performed. Histopathologic evaluation demonstrated malignant glandular epithelial cells with focal signet ring-like appearance, present mainly in the dermis, with focal epidermotropism and folliculotropism. Immunohistochemical testing showed reactivity with TTF-1, CK7, Napsin, and CEA, while CK5/6 was negative, supporting the interpretation of metastatic lung adenocarcinoma. Approximately 1-2% of patients with lung cancer, including adenocarcinoma, develop metastasis to the skin which could be associated with poor prognosis. Rarely, cutaneous metastasis might be the first manifestation of the disease. The clinical presentation is non-specific and could generate a broad differential diagnosis of benign and malignant neoplasms. Histopathologically, malignant glandular structures are seen in the dermis, and on very rare occasions in the epidermis, which could raise the differential diagnosis of primary cutaneous adnexal carcinomas. Accurate diagnosis requires careful clinical correlation with appropriate utilization of ancillary immunohistochemical stains.

Financial Disclosure:
No current or relevant financial relationships exist.