Cytomorphologic features characteristic of tumor stages of thymomas

The cytologic findings of the tumor cells characteristic of the stages of t hymomas were investigated to assess the invasiveness of the tumors. Forty-s ix patients with thymoma who underwent extensive thymectomy without preoper ative corticosteroid therapy were included in this study. The histologic su btypes included 18 round/oval, 20 mixed, and 8 spindle type. The stages of thymoma classified according to Masaoka's clinicopathological classificatio n included 16 stage I, 20 stage II, 6 stage III, 2 stage IVa, and 2 stage I Vb, and myasthenia gravis was recognized in 5 patients. Cytologic findings were retrospectively analyzed in the Papanicolaou-stained stamp smears obta ined from the cut surfaces of thymoma specimens. Morphometry of the epithel ial tumor cells using Cosmozone-1A was performed to evaluate the validity o f our cytologic categories. Compared with the cytologic findings of stage I or II thymomas, those of epithelial tumor cells in stage III or IV more fr equently showed necrotic background (50.0%-stage III or IV vs 11.1%-stage I or II, p=0.006), large clusters of epithelial tumor cells (70.0% vs 36.1%, p=0.055), marked nuclear enlargement (90.0% vs 52.7%, p-0.033), marked ani sokaryosis (100% vs 52.7%, p=0.006), marked nuclear polymorphism (40.0% vs 5.5%, p=0.004), hyperchromasia (50.0% vs 11.4%, p=0.007) and prominent nucl eoli (50.0% vs 16.6%, p=0.028) whereas no significant correlation was obser ved between cytologic findings and tumor volume. Morphometric studies of th ymoma tumor cells revealed that the nuclear size (mean values, 78.8 mum(3)- stage III or IV vs 58.2 mum(3)-stage I or II), the coefficient of variation of the nuclear size (0.326 vs 0.282), and the nuclear rotundity (0.849 vs 0.858) differed significantly between the two categories (p<0.05). Our find ings demonstrated that there were significant differences between the cytol ogic findings of epithelial tumor cells of stage I or II thymomas and those of stage III or IV thymomas, and that the cytologic findings of thymoma tu mor cells appear to be useful for distinguishing between noninvasive and in vasive thymomas.