Application of SEM-EDX for the Identification of Malignant Cells in Bronchial Brush Cytology: A Prospective Study

Scanning electron microscopy (SEM) provides ultra-high-resolution imaging, and when combined with energy-dispersive X-ray spectroscopy (EDX), it enables quantitative elemental analysis. We aimed to evaluate whether SEM-EDX provides quantitative criteria for differentiating between malignant and benign cells in cytology specimens. In this prospective observational study, 49 cytology specimens obtained via bronchial brushing of peripheral pulmonary lesions between April 2021 and March 2022 were analyzed using a tabletop SEM (TM4000PlusII, Hitachi High-Tech). For each specimen, the phosphorus characteristic X-ray signal counts (P-counts) and nuclear areas (N-areas) were quantified in malignant and normal cells. Cases were classified into four distribution patterns based on statistically significant differences in P-counts and N-areas: (I) increased P-counts only, (II) increased P-counts and N-areas, (III) increased N-areas only, or (IV) no significant differences. All 47 malignant cases demonstrated significantly higher P-counts and/or N-areas than normal cells. Patterns I, II, and III were observed in 3 (6.4%), 37 (78.7%), and 7 (14.9%) cases, respectively; no cases met the Pattern IV criteria. The two benign cases showed distributions overlapping those of normal cells. SEM-EDX distinguished between malignant and non-malignant cells by quantifying the nuclear phosphorus content and area, supporting its potential role as an adjunct diagnostic tool in cancer cytopathology.