Adverse Prognostic Impact of Transitional and Pleomorphic Patterns in Pleural Nonepithelioid Mesothelioma: Insights From Comprehensive Analysis and Reticulin Stain.

Context.—: Mesothelioma subtyping into epithelioid and nonepithelioid categories plays a crucial role in prognosis and treatment selection, with emerging recognition of the impact of various histologic patterns.
Objective.—: To investigate the prognostic implications of transitional and pleomorphic patterns in sarcomatoid mesothelioma.
Design.—: A total of 132 mesothelioma cases (87 biphasic, 45 sarcomatoid) were analyzed. Histologic slides were assessed, treatment data collected, and cases categorized into predominant epithelioid or sarcomatoid patterns. The sarcomatoid mesotheliomas were classified into usual, pleomorphic, and transitional patterns, with reticulin staining for the latter. Statistical analysis included Cox regression and Kaplan-Meier methods.
Results.—: Younger age (P = .02) and receiving therapy (P < .001) correlated with improved survival for both histotypes. Advanced stage was associated with shorter survival in sarcomatoid cases (P = .02). Predominant epithelioid pattern in biphasic cases led to longer survival (P < .001). Transitional and pleomorphic patterns were indicative of worse prognosis, with significantly lower survival in cases with both patterns than with usual sarcomatoid (P = .046). Multivariate analysis identified independent survival factors, including predominant epithelioid component in biphasic mesothelioma (P = .001) and chemotherapy (P < .001).
Conclusions.—: Histologic subtyping in mesothelioma plays a pivotal role in prognosis. Transitional and pleomorphic patterns, even in low percentages, indicate poorer outcomes. This study highlights the need for standardized diagnostic support and suggests the potential utility of histochemical staining in identifying more aggressive morphologic aspects. Recognizing the significance of these patterns can guide treatment decisions and patient care strategies.
(© 2024 College of American Pathologists.)