Skin Metastasis of an Occult Primary Bronchopulmonary Disease: A Case Report and Literature Review.

Cutaneous metastases of pulmonary origin are rare but clinically significant, typically indicating advanced disease with a poor prognosis. They may occasionally reveal an occult lung cancer, as illustrated by the case reported here. We report the case of a 78-year-old man, a former heavy smoker, who presented with a rapidly growing, ulcerated, exophytic nodule on the anterior chest wall. Skin biopsy revealed a poorly differentiated adenocarcinoma, with negative thyroid transcription factor-1 (TTF-1) and Napsin A staining, raising diagnostic difficulty regarding the primary origin. Chest CT subsequently identified a 4.1 cm tumor of the right lower lobe, and bronchoscopic biopsy confirmed a bronchial adenocarcinoma. Staging revealed disseminated disease (cT2b cN1 cM1c, Stage IVB) with cerebral, adrenal, and bone metastases. A multidisciplinary tumor board recommended whole-brain radiotherapy (30 Gy in 10 fractions) combined with palliative chemotherapy (cisplatin-gemcitabine), with stable disease observed at six months of follow-up. This case underlines the limitations of TTF-1 and Napsin A negativity in excluding a pulmonary origin, particularly in poorly differentiated tumors, and highlights the value of an integrated clinical, radiological, morphological, and immunohistochemical approach. Management of extensively disseminated disease remains essentially palliative; surgery has no impact on survival and is reserved for palliative or diagnostic indications.