Analysis of cell cycle regulator proteins in encapsulated thymomas

Although survival of encapsulated thymomas is usually good, some patients present a higher incidence rate of recurrence and a shorter long-term survival. Abnormalities in the components of cell cycle checkpoints are extremely common among virtually all neoplasms. In this study, three components of the cell cycle machinery (i.e., p21, p27 and p53) were examined in a series of well-characterized encapsulated thymoma specimens to analyze coregulation and influence on recurrence and survival.

Sixty-eight consecutive patients with thymoma were operated in our center from 1987 to 2000. Expression of p53, p21, and p27 was studied in specimens from 25 encapsulated thymomas using immunohistochemistry. Generic factors and gene expression influencing the probability of recurrence were studied. Positive expression was dichotomized defining positive when present in more than 5% of tumor cells. Mean follow up was 85.9 months; clinical data about recurrence were recorded.

Univariate analysis suggests that positive p53 (P < 0.05), negative p21 (P = 0.01), and especially negative p27 expressions (P = 0.001) significantly correlate with poor prognosis for disease-free survival. Multivariate Cox regression analysis suggests that negative p27 immunohistology is the only significant variable for poor prognosis (P = 0.03; odds ratio, 0.08; 95% confidence interval, 0.01-0.88).

These results show that loss of control of cell cycle checkpoints is a common occurrence in thymomas and support the idea that functional cooperation between different cell cycle inhibitor proteins constitutes another level of regulation in cell growth control and tumor suppression.