DNA ploidy in thymoma and associated multiple primary malignancies in the same patient.

Thymoma is an uncommon neoplasm derived from thymic epithelium. It is located in the anterosuperior mediastinum. Thymoma may be associated with different types of additional primary malignancies; however, colorectal adenocarcinoma and thyroid cancer appear to be most common. A case is presented of a 63-year-old woman with type A thymoma and two other primary carcinomas of the breast and colon that were previously diagnosed. The patient underwent surgery due to metastatic colon cancer of the lung and yet another primary tumor was found in the mediastinum, later diagnosed as thymoma. A normal diploid pattern was found in the samples of thymoma and colon carcinoma, whereas those of breast carcinoma and metastatic tumor of the lung showed aneuploidy. On the basis of previous studies and our case, it is concluded that the occurrence of extrathymic malignancies does not correlate with the biologic behavior and DNA ploidy of thymoma.