Tumor-to-tumor metastasis: Pulmonary adenocarcinoma metastatic to SchwannomaThe coexistence of multiple primary malignant tumors in the same host is not unusual; however, tumor-to-tumor metastasis is rare.According to previous publications, the most common recipient tumor is renal cell carcinoma, and lung carcinoma is the most frequent donor site.According our bibliographic search we are presenting the first published case of primary pulmonary moderately differentiated adenocarcinoma metastatic to a schwannoma, demonstrated with Thyroid Transcription Factor 1 (TTF-1); immunostaining has become an important tool for guiding diagnosis of adenocarcinoma.