Khoór, András

Aims Lymphangioleiomyomatosis (LAM) is a PEComa that primarily affects premenopausal women and is associated with the cystic destruction of the lung. Although smooth muscle and melanocytic markers can be helpful, histologic diagnosis of LAM remains challenging, especially in small biopsies. Glycoprotein non‐metastatic melanoma protein B (GPNMB) expression has recently been identified as a highly specific and sensitive immunohistochemical marker for PEComas. Nevertheless, only a few LAM cases have been studied so far. The aim of this study was to assess the utility of GPNMB immunohistochemistry as an ancillary marker in a larger cohort of LAM samples. Methods and results Immunohistochemistry for GPNMB was performed on cases of LAM ( N = 15), potential differential diagnostic mimics ( N = 30) and normal lung tissue ( N = 2). Immunohistochemistry was assessed using the H‐score method; an H‐score above 100 was considered ‘high’. All LAM cases showed strong cytoplasmic expression, with cell membrane accentuation in some areas. In contrast, differential diagnostic mimics were either negative or only weakly positive. Normal lung parenchyma was negative for GPNMB; however, weak‐to‐moderate expression was seen in alveolar macrophages in both the normal and diseased lung tissues in most cases. Considering only ‘high’ positivity, GPNMB immunohistochemistry showed 100% sensitivity and specificity for the diagnosis of LAM in our cohort. Conclusions Based on its 100% sensitivity and specificity, GPNMB appears to be a highly valuable immunohistochemical marker for the diagnosis of pulmonary LAM. Besides its diagnostic value, the membrane positivity of GPNMB on LAM cells may predict a response to glembatumumab vedotin, an antibody‐drug conjugate targeting GPNMB.

Pulmonary Langerhans cell histiocytosis (PLCH) is a rare inflammatory condition that mostly affects lungs in smokers. On imaging, it usually presents as multiple, upper lobe predominant, solid, and cavitary nodules, but presentation as solitary pulmonary nodule (SPN) is rare. We describe a case of SPN seen on low-dose lung cancer screening CT (LDCT) that was FDG avid on PET/CT. Given concern for malignancy, lobectomy was planned if intraoperative frozen section was consistent with malignancy. Lobectomy was performed based on frozen section; however, on formal pathology review, the nodule was ultimately found to be PLCH. This case illustrates an atypical presentation of PLCH as a solitary nodule. Furthermore, it helps demonstrate how rare etiologies (like PLCH) may be more frequently encountered and should be considered in the differential diagnosis for solitary lung nodules, especially in the era of lung cancer screening.

COPA syndrome is a newly discovered, rare genetic autoimmune disorder, which can affect the lungs, joints, and kidneys. It is difficult to recognize, and the survival benefit of lung transplantation for these patients is not yet known. We present a case of a 24-year-old woman who received bilateral lung transplant for COPA syndrome. At 15 months posttransplant, her pulmonary function is stable with no episodes of acute cellular- or antibody-mediated rejection and no evidence of disease recurrence.