Application of SEM-EDX for the identification of malignant cells in bronchial brush cytology: a prospective study

Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX) enables quantitative elemental analysis. We aimed to evaluate whether SEM-EDX provides quantitative criteria for differentiating between malignant and benign cells in cytology specimens. This prospective study analyzed 49 cytology specimens obtained via bronchial brushing of peripheral pulmonary lesions between April 2021 and March 2022 using a tabletop SEM (TM4000PlusII, Hitachi High-Tech); 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 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 Pattern IV criteria. The two benign cases exhibited distributions overlapping normal cells. Although the number of benign cases was limited, these findings provide preliminary evidence that SEM-EDX may serve as a quantitative adjunct for cytologic evaluation, suggesting potential research relevance and future clinical applicability, warranting further validation in larger cohorts including benign and reactive lesions.