Metastatic Sarcomatoid Lung Cancer: A Rare Cutaneous Spindle Cell Neoplasm.

Cutaneous spindle cell neoplasms can be a diagnostic challenge and may require extensive immunohistochemical staining. The differential diagnoses include melanoma, squamous cell carcinoma, atypical fibrous xanthoma, leiomyosarcoma, dermatofibrosarcoma protuberans, and cutaneous metastases of visceral neoplasms. The authors present a patient with rapidly growing cutaneous nodules in the setting of widespread metastatic disease with clinical suspicion of pulmonary origin. A biopsy demonstrated a poorly differentiated dermal spindle cell neoplasm without overlying epidermal attachment. Immunohistochemical staining demonstrated positivity for cytokeratin wide spectrum screening, cytokeratin-7, CD10, and D2-40. Negative staining was noted for S100, MART-1, SOX-10, CD31, CD45, synaptophysin, chromogranin, CD56, CEA, calretinin, WT-1, HBME-1, TTF-1, and p63. Overall, clinical presentation, histologic pattern, and immunohistochemical profile were consistent with cutaneous metastases of sarcomatoid carcinoma originating in the lung. Diagnosis of sarcomatoid carcinoma can be challenging and requires a carefully select panel of immunohistochemical markers to aid in the accurate diagnosis of this uncommon malignancy and even more rare cutaneous metastatic disease. Sarcomatoid cancer of the lung should be considered in the differential diagnosis of metastatic malignant spindle cell neoplasms.