Primary thymic epithelial neoplasms in children.

Primary epithelial neoplasms of the anterior mediastinum in children are very rare. We have studied 10 cases of thymic epithelial neoplasms in children aged 16 years or less and correlated their histologic features with the clinical outcome. The patients' ages ranged from one to 16 years (mean: 10.2); with a male:female ratio of 1.5:1. Nine patients had symptoms attributable to their tumors; one was asymptomatic. Four patients presented in clinical stage I, one in stage IIb, and five in stage IVb. Histologically, the tumors comprised a heterogenous group displaying a range of morphologic appearances: one tumor had the classic features of lymphocyte-rich thymoma of the adult; four were of the lymphocyte-rich type with associated unusual stromal features; two were spindle cell thymomas with cytologic and architectural atypia; and three displayed obvious cytologic features of malignancy (i.e., thymic carcinoma); two in the last group showed features of small cell carcinoma, and the other was an undifferentiated/anaplastic carcinoma. The epithelial nature of the tumors was supported in six cases by positive staining of the tumor cells with keratin antibodies and in two cases by electron microscopic demonstration of desmosomes and intracytoplasmic bundles of tonofilaments within the tumor cells. The prognosis for these patients correlated well with the degree of atypicality exhibited by the epithelial components; it was very poor in patients with small cell and undifferentiated/anaplastic carcinoma (8 months average survival), better for those with atypical spindle cell thymomas (multiple recurrences and metastases but no fatalities over a 15- to 72-month period), and best in those with lymphocyte-rich thymomas without cytologic atypia (no recurrences or metastases over an 8-month to 3-year follow-up).