title: WHO types A and AB thymomas: not always benign.
abstract: The 2004 WHO classification of thymic tumors recognizes five major subtypes of thymomas and thymic carcinoma. Subtypes A and AB thymomas are purported to be benign neoplasms, although prior studies have suggested a potential for malignant behavior. The purpose of this study was to assess the clinical behavior of A and AB thymomas identified from a large institutional pathologic database. A retrospective slide review of 500 thymic epithelial tumors identified 71 (∼ 14%) cases of types A and AB thymomas. Clinical history and follow-up information were obtained through retrospective chart review. There were 38 and 33 cases of types A and AB thymomas, respectively. Complete follow-up data were available in 37 (52%) cases. Eighteen (49%) patients (type A, n=9 and type AB, n=9) had evidence of recurrent/metastatic disease at an average of 62 months (range from 6 to 244 months) after initial diagnosis. Survival curves for patients with types A and AB thymomas, with and without recurrences, show a statistically significant difference (P=0.001 and 0.005, respectively). Analysis of this large cohort confirms the potential for subtypes A and AB thymomas to show malignant behavior. Long-term clinical monitoring, therefore, appears to be justified in these cases. This study also shows the poor correlation between the WHO classification and tumor behavior.
authors.affiliation: Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Rohit K
authors.initials: RK
authors.lastname: Jain
authors.forename: Rutika J
authors.initials: RJ
authors.lastname: Mehta
authors.forename: John D
authors.initials: JD
authors.lastname: Henley
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Kesler
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Loehrer
authors.forename: Sunil
authors.initials: S
authors.lastname: Badve
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011379:Prognosis; D012189:Retrospective Studies; D013945:Thymoma / Q000145:classification / Q000401:mortality / Q000473:pathology*; D013953:Thymus Neoplasms / Q000145:classification / Q000401:mortality / Q000473:pathology*; D014944:World Health Organization