Clinicopathological Features, Cell Membrane and Cytoplasmic Immunostaining of Ki‐67 MIB‐1 in the Diagnosis of Pulmonary Sclerosing Pneumocytoma

Pulmonary sclerosing pneumocytoma (PSP) is a rare benign tumor with varied histological morphology. The rarity and morphological heterogeneity of PSP may pose diagnostic challenges for pathologists. In this study, we retrospectively reviewed the clinicopathological features of 36 PSPs, and explored the diagnostic value of Ki-67 MIB-1 in PSPs. Among these PSPs, there was a significant female predominance. Microscopically, the tumors were all composed of a dual-cell population, and had a combination of at least two of the four growth patterns, i.e. papillary, sclerotic, solid and hemorrhagic. Immunohistochemically, the surface cells were TTF1 (+)/CK7 (+), while the stromal cells were TTF1 (+)/CK7 (-). Ki-67 MIB-1 highlighted the immunostaining of cell membrane and cytoplasmic in tumor cells when performed at room temperature (20°C-25°C) using the Benchmark ULTRA system. Such a staining pattern of MIB-1 was significantly higher in PSPs than that in NSCLCs (p < 0.001). This is helpful for the differential diagnosis, especially for core biopsy specimens which are often limited for sampling. Basing on the careful morphological observation and TTF-1/CK7 immunostaining could diagnose most PSPs, while a unique cell membrane and cytoplasmic staining of MIB-1 performed at room temperature could be a useful adjunct to the accurate diagnosis of PSP.