The prognostic importance of histologic classifications of thymic epithelial neoplasms is controversial. Evidence suggests that difficulties in reproducibility affect prognostic studies. According to the World Health Organization (WHO) classification, two thoracic pathologists independently classified 80 cases of type A or B3 thymoma and thymic carcinoma.
A recent article in Human Pathology by Mayo Clinic, first author Anja Roden, M.D., addresses the diagnostic significant of cell kinetic parameters in type A or B3 thymoma and thymic carcinomas. Ki-67 labeling index (LI) was used to identify cutoff points between WHO types. Recursive partitioning (Rpart) and ad hoc methods separated the data points.
According to the article, the pathologists disagreed on histologic type in 14 cases. In 11 of 14 cases with available Ki-67, the Rpart method predicted the WHO type; in 7 of 14 cases, the ad hoc method predicted the WHO type. In conclusion, Ki-67 LI is helpful in differentiating thymic epithelial neoplasms, with Ki-67 LI less than 2 percent and greater than or equal to 13.5 percent distinguishing type A thymoma and thymic carcinoma, respectively.
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*Additional Mayo Clinic authors include Stephen Cassivi, M.D., Randolph Marks, M.D., Marie Aubry, M.D., E. Yi, Sarah Jenkins, and Janis Donovan.