Tumor-to-tumor metastasis: an unusual case of breast cancer metastatic to a solitary fibrous tumor.

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that most commonly involves the visceral or parietal pleura, but that has also been described arising from virtually all organs. This neoplasm exhibits rich vascularity, a characteristic it shares with renal cell carcinoma, making these tumors especially suitable for harboring metastases. We present a case of a 64-year-old woman with history of right breast cancer treated six years previously and who presents with a left pulmonary SFT containing metastatic invasive ductal breast carcinoma as well as a synchronous contralateral primary adenocarcinoma of the lung. The literature on tumor-to-tumor metastasis is then reviewed.