Evidence-based pathology and the pathologic evaluation of thymomas: transcapsular invasion is not a significant prognostic feature.

CONTEXT: Evaluation of transcapsular invasion is currently considered very important in the pathologic examination of thymomas. However, recent studies have questioned the prognostic value of stratifying thymoma patients into stage I and II disease. Evidence-based pathology promotes the use of systematic reviews of literature and meta-analysis of data to synthesize the results of multiple publications.

OBJECTIVE

To analyze the data in the literature regarding the prognostic importance of transcapsular invasion in thymoma stage I and II.

DESIGN

A systematic review of the English literature was carried out for "thymoma," "stage," and "prognoses." Case reports, case series with fewer than 10 cases, and studies with follow-up periods shorter than 5 years were excluded. Twenty-one retrospective publications reporting the experience with 2451 thymomas were selected for review, including 1419 stage I and 1032 stage II patients. Meta-analysis was performed, and possible publication bias was studied with funnel plots of precision and various statistics.

RESULTS

Meta-analysis yielded no significant differences in disease-free or overall survival rates in stage I and II thymoma patients. Funnel plots of precision and statistical tests such as the Egger regression intercept test showed no significant publication bias.

CONCLUSIONS

The lack of significant differences in the prognosis of patients with stages I and II thymoma suggests that evaluation of transcapsular invasion is of no clinical value in tumors that lack invasion of neighboring organs or the pleura. The data regarding the prognosis of stage II thymoma patients is somewhat heterogenous, with only some individuals having been treated with radiation therapy, suggesting the need for future randomized controlled trials.