[A clinicopathological study of thymomas, with special reference to evaluation of malignant grade by morphometric...

To determine the factors influencing the extent and recurrence of thymoma, 31 cases of thymoma who had undergone complete resection were analyzed clinicopathologically with special reference to the nuclear area of epithelial cells. The mean tumor size and incidence of recurrence of stage III thymomas were significantly larger and higher than those of stage I thymomas. The nuclear area of epithelial cells of stage III thymomas (72.9 +/- 29.2 micron 2) was significantly larger than that of stage I thymomas (48.4 +/- 13.2 micron 2) or stage II thymomas (49.4 +/- 11.6 micron 2). The nuclear area of thymomas with recurrence (70.2 +/- 21.5 micron 2) was significantly larger than that of those without recurrence (50.2 +/- 12.8 micron 2). In 16 cases who were followed up for 5 years or more, the nuclear areas were over 50 micron 2 in all thymomas with recurrence, while in 8 of 11 thymomas without recurrence it was under 50 microns 2. These results indicated that the tumor size and nuclear area increased step-wisely in association with the advance of clinical stage and that the incidence of recurrence was related to not only clinical stage but also nuclear area. Thymomas with large nuclear area (over 50 microns 2) are considered to be a high-risk group of recurrence and should be carefully followed up.