Correlation of the WHO schema for the classification of thymic epithelial neoplasms with prognosis: a retrospective study of 90 tumors.

A series of 90 thymic epithelial tumors were reviewed and classified by histopathologic characteristics into the three major categories (A, B, and C) recognized by the WHO schema. Each tumor type was correlated with patient characteristics and clinical data (age, sex, presence of myasthenia gravis, tumor size and invasiveness, and completeness of resection), and with outcome (survival, recurrence, and metastasis). All tumors were categorized by the WHO schema. Myasthenia gravis was present in 32 patients, mostly young and with type B thymic epithelial tumors. Tumors were invasive in 56% of cases, but resection was total in 67% of patients and only partial in the rest. Five factors were shown by univariate analysis to be associated with a favorable prognosis: presence of myasthenia gravis (p = 0.0389), younger age (p = 0.0022), completeness of resection (p = 0.0001), noninvasiveness (p = 0.0138), and tumor type A or B, as opposed to type C (p = 0.0001). Prognosis for types A and B was not significantly different, suggesting that the subtypes of types A and B thymic epithelial tumors should be regarded as a morphologic continuum rather than as distinct histologic variants.