Pulmonary Granular Cell Tumors: A Study of 4 Cases Including a Malignant Phenotype

Granular cell tumors are lesions of Schwannian phenotype that most frequently arise in the skin, breast, and tongue. Pulmonary granular cell tumors (pGCTs) are exceedingly rare and only a handful of cases worldwide have been reported as malignant. We report here a series of 4 pGCTs, including an extremely rare case of a malignant pGCT which underwent next-generation sequencing to identify a novel pathogenic mutation. We are the first to report any prognostic data and response to treatment. Consistent with granular cell tumors of other primary sites, the majority of pGCTs (75%) were deemed histologically and biological benign without metastasis or recurrence after resection (mean follow-up, 750 d). pGCTs occurred predominantly in women (75%) with a mean age of 57 years (range, 49 to 66 y) and variable smoking history. Notably, 2 women also developed an associated lung carcinoma (adenocarcinoma and small cell carcinoma). We also report here an exceedingly rare case of a 51-year-old nonsmoker woman diagnosed with a malignant pGCT. She presented with a 6.4×6.1×4.4 cm infrahilar left lower lobe mass with extrinsic compression and obstruction of the left mainstem on enhanced computed tomography. Pathology of the resection specimen confirmed a pGCT composed of sheets of tumor cells with pleural, pericardial, and diaphragmatic metastases. Molecular analysis by next-generation sequencing failed to yield any driver mutations common to primary lung adenocarcinomas. Only 2 previous malignant pGCTs have been reported; our case revealed a novel pathologic ATM mutation.