Tumor-to-tumor metastasis: maxillary sinus adenoid cystic carcinoma metastasizing to double primary lung adenocarcinoma.

Tumor-to-tumor metastasis is a rare occurrence. The most frequent metastatic donor is lung cancer, and the most frequent recipient is renal cell carcinoma. Here we present a patient in whom lung cancer served as a metastatic recipient and maxillary sinus adenoid cystic carcinoma acted as a metastatic donor. This patient has double primary lung cancer, which increased the complexity of this case.