Elastic Staining Features in Pulmonary Non-Mucinous Adenocarcinoma and Associated In Situ Lesions: Diagnostic Implications.

Elastic staining may aid in the diagnosis of pulmonary non-mucinous adenocarcinoma and its in situ lesions. This study evaluated elastic staining patterns and their diagnostic utility in a multi-cohort series. Elastic staining was performed in 120 lesions, including a principal cohort (n = 60), an internal validation cohort (n = 30), an external validation cohort (n = 30), and an interobserver agreement cohort (n = 40). Staining patterns were analyzed and their impact on diagnostic accuracy was assessed. Four elastic staining patterns were identified: a point-and-linear pattern, an intensified point-and-linear pattern, a disorderly thickened and recoiled pattern with continuous and discontinuous variants, and a decreased or disappeared pattern. All adenocarcinoma in situ lesions and the in situ components of minimally invasive adenocarcinoma and invasive adenocarcinoma demonstrated the continuous disorderly thickened and recoiled pattern. The decreased or disappeared pattern was observed in the majority of invasive adenocarcinomas and in all invasive components of minimally invasive adenocarcinoma, whereas a subset of invasive adenocarcinomas exhibited the discontinuous variant associated with extensive carcinomatous collapse. Non-neoplastic lesions displayed a point-and-linear pattern, with an intensified point-and-linear pattern observed in regions of iatrogenic or mechanical collapse. No significant differences were identified between validation cohorts (P > 0.05). Diagnostic accuracy and histologic identification improved with the use of elastic staining among both trainee and general pathologists, and interobserver agreement was high (Kappa = 0.945). Overall, elastic staining represents a useful adjunct for improving diagnostic accuracy and histologic classification of pulmonary non-mucinous adenocarcinoma and its in situ lesions.