Histologic types of thymoma associated with pure red cell aplasia: a study of five cases including a composite tumor of organoid thymoma associated with an unusual lipofibroadenoma.

The histologic type of thymomas associated with pure red cell aplasia (PRCA) has generally been regarded to be predominantly the spindle cell type. The 5 thymomas associated with PRCA we studied showed various histologic types and none of them was a spindle cell thymoma. Some cases reported as spindle cell thymoma associated with PRCA in the literature might not be spindle cell type. The discrepancy could be due to the lack of consensus in the histologic classification of thymomas in the past. Our study showed that thymomas associated with PRCA lacked a strong correlation with a particular histologic type and the pathogenesis of PRCA associated with thymoma did not seem to be related to the histologic type. One of our cases was an unusual composite tumor of an organoid thymoma (WHO type B1) and a hitherto undescribed "lipofibroadenoma." The clinical outcome was influenced by the invasive character and the histologic type of the thymoma.