Classification of thymic neoplasms: Observations on the WHO 1999 classification based on 56 cases

Background: The World Health Organization (WHO), in 1999, laid down histological criteria for thymoma sub-classification (Type A, AB, B1, B2, B3 and C). This study aims to assess the ease of application of this classification and to evaluate any relationship with the clinical stage.
Material and Methods: A total number of 56 cases from the Tata Memorial Hospital, Mumbai were studied.
Results: The age of the patients ranged from 17 to 71 years (mean 48.6 years) and the male to female ratio was 3:1. The number of cases in each of the WHO tumour types were Type A-10, Type AB-20, Type B1-6, Type B2-11, Type B3-3, and Type C-6 cases. Invasive tumours were seen in 25%, 23%, 75%, 60%, 100% and 100% of Type A, AB, B1, B2, B3 and C tumours, respectively.
Conclusion: It can be concluded that the WHO Classification is histologically reproducible and there is a good correlation between the WHO subtypes and tumour invasiveness.