Tumor-to-tumor metastasis: breast cancer metastatic to thymic epithelial tumor.

Tumor-to-tumor metastasis is a rare phenomenon, with around 150 cases being reported in the literature. Breast cancer is the second most commonly reported donor tumor after lung cancer, but thymic epithelial tumors have never been reported as recipient tumors. Furthermore, the thymus is rarely affected by metastases. To our knowledge, the present report is the first case of breast cancer metastatic to thymic epithelial tumor.