Thymoma

Histological classification of thymoma is not sufficient to distinguish biologically indolent thymomas from thymomas that exhibit aggressive clinical behavior. Although some thymoma histological types are more likely to be clinically aggressive, treatment outcome and the likelihood of recurrence appear to correlate more closely with the invasive/metastasizing properties of the tumor cells.[25,35] Therefore, some thymomas that appear to be relatively benign by histological criteria may behave very aggressively. Independent evaluations of both tumor invasiveness (using staging criteria) and tumor histology may be combined to predict the clinical behavior of a thymoma.

Both histological classification of thymomas and stage may have independent prognostic significance.[35,36] A few series have reported the prognostic value of the WHO classifications. Two large retrospective analyses, one with 100 thymoma cases and the other with 178 thymoma cases, showed that disease-free survival at 10 years varied (see Table 1).[37,38] In these series, stage and complete resection were significant independent prognostic factors. Another analysis reported on 273 thymoma patients who were treated over a 44-year period. See Table 1 for the 20-year survival rates.[35]