[Histopathological diagnosis of pulmonary sclerosing pneumocytoma in needle biopsy specimens]

Objective: To investigate the diagnostic features of pulmonary sclerosing pneumocytoma (PSP) in needle biopsy specimens so as to improve the preoperative diagnostic accuracy and to prevent misdiagnoses. Methods: A total of 79 needle biopsy cases confirmed as PSP in surgical resection specimens were collected in the First Affiliated Hospital of Zhengzhou University, Zhengzhou, China from January 2015 to January 2023. A retrospective analysis was conducted to investigate the clinical, pathological, and immunohistochemical characteristics of PSP. Results: Among the 79 cases, there were 8 males and 71 females, with an age range of 14 to 67 years (median 47 years). Among the 79 needle biopsy cases of PSP, 5 cases were initially misdiagnosed as adenocarcinoma and 1 as carcinoid preoperatively, while the remaining 73 cases were correctly diagnosed. 84.8% (67/79) of the PSP presented with well-defined, homogeneous, solitary solid tumors on chest imaging. Morphologically, 26.6% (21/79) of the PSP mainly showed a single histological component, 67.1% (53/79) contained two histological components, and 6.3% (5/79) contained three histological components. There were no cases containing all four histological components simultaneously. The tumor was composed of cuboidal cells on the surface and round cells in the stroma and lacked significant cytological atypia and mitotic figures. Some cases exhibited variations in histology and cellular morphology, such as glandular spaces (58.2%, 46/79), sclerotic papillae (46.8%, 37/79), hypercellularity (16.5%, 13/79), and cytological atypia (24.1%, 19/79). Immunophenotyping indicated that both tumor cell types expressed TTF1, EMA and β-catenin, while surface cells expressed pan-cytokeratin and Napsin A, and stromal cells expressed vimentin. In some cases, ER and PR were also expressed. Conclusions: When diagnosing PSP in needle biopsy specimens, the key to avoiding misdiagnosis is recognizing the presence of dual-cell populations within the tumor. The useful clues include presence of cellular papillae, mild cellular atypia, morphological diversity, interstitial foam-like cell aggregates, and prominent background hemorrhage and sclerosis. The characteristic immunophenotype and middle-aged female predilection are also helpful for the diagnosis of PSP.