S-100-Negative malignant pulmonary granular cell tumor: A case report.

Malignant pulmonary granular cell tumor (GCT) is extremely rare and difficult to distinguish from benign GCT. Most GCTs are neural-type and express S-100. However, a small subset of tumors sub-classified as the non-neural type do not express S-100. We report a case of malignant non-neural-type GCT in the lungs. A 77-year-old woman felt chest discomfort and dyspnea in July 2019. She had never smoked and had no medical history other than hypertension and diabetes mellitus. She was initially evaluated at a local hospital. Flexible bronchoscopy showed total occlusion of the right main bronchus by a mass-like lesion. Biopsy of the mass lesion revealed chronic inflammation. The patient visited for re-evaluation in September 2019. Rigid bronchoscopy showed worsening of the total obstruction of the right main bronchus by a tumor mass, such that the carina was not visible. Additionally, endobronchial nodules were observed on the medial side of left main bronchus. The tumor masses of both main bronchi were removed by bronchoscopic intervention, but the right main bronchus was not opened. Biopsy revealed malignant GCT, favoring the non-neuronal type (S-100-negative). We report an extremely rare case of malignant pulmonary GCT negative for S-100 in immunohistochemistry. In this case, surgical resection was not possible because the tumor was diagnosed at a fairly advanced stage and had spread to involve the contralateral main bronchus. The patient chose to be treated at another hospital and was thereafter lost to follow-up.