LONG-TERM SURVIVAL OF THYMOMA PATIENTS BY HISTOLOGIC PATTERN AND PROLIFERATIVE ACTIVITY

We performed DNA flow cytometry and analysis of the argyrophilic nucle olar organizer regions (AgNORs) in formalin-fixed, paraffin-embedded s ections from 60 surgically resected thymomas. The results were correla ted with histologic pattern, stage, associated clinical features, and survival to assess which parameters could best predict prognosis. On u nivariate analysis, the 10-year survival rates were 86% for predominan tly lymphocytic type but only 42% for predominantly epithelial, mixed lymphoepithelial, or spindle cell thymomas (p = 0.006); survival rates were 85% for noninvasive but only 34% for invasive thymomas (p = 0.00 02); 73% for diploid but only 38% for aneuploid cases (p = 0.005); 88% for thymomas with 5.75 AgNORs per cell or fewer but only 34% for thym omas with more than 5.75 AgNORs per cell (p < 0.0001). On multivariate survival analysis, tumor stage (p < 0.001) and AgNOR counts (p = 0.00 9) retained independent prognostic significance. The 16 patients with predominantly lymphocytic type and 5.75 AgNORs per cell or fewer were all alive at the end of the observation period. In conclusion, the his tologic type of the American classification and the proliferative acti vity evaluated by AgNOR analysis are the best predictors of long-term survival for patients with thymoma. Both predictors can be easily eval uated in the same histologic section, are highly reproducible, and per mit identification of a group of patients with a favorable outcome reg ardless of other clinicopathological features.