Pulmonary Sarcomatoid (Pleomorphic) Carcinoma Presenting As Secondary Spontaneous Pneumothorax in Diffuse Cystic Lung Disease: A Case Report.

Pulmonary sarcomatoid carcinoma is a rare and aggressive subtype of non-small cell lung cancer associated with poor prognosis and atypical clinical presentations. Spontaneous pneumothorax as an initial manifestation is exceedingly uncommon and may obscure the underlying diagnosis, particularly in patients with diffuse cystic lung disease. This report describes a case of pulmonary sarcomatoid (pleomorphic) carcinoma presenting with secondary spontaneous pneumothorax in the setting of diffuse cystic lung abnormalities, highlighting the diagnostic challenges encountered and the importance of maintaining suspicion for malignancy in atypical presentations. Early tissue diagnosis, multidisciplinary evaluation, and molecular profiling played key roles in guiding definitive management. This case underscores the need to consider lung cancer in patients presenting with spontaneous pneumothorax and atypical parenchymal findings, as timely recognition may permit curative-intent treatment and biomarker-informed systemic therapy in this aggressive malignancy.