Tumor-to-Tumor Metastasis of Epidermal Growth Factor Receptor (EGFR)-Mutated Lung Adenocarcinoma to a Meningioma 14 Years After Curative Lobectomy: A Case Report.

Tumor-to-tumor metastasis is a rare oncologic phenomenon in which one primary malignancy metastasizes into another distinct neoplasm. While meningiomas are the most common recipients, this route of recurrence has not been reported in epidermal growth factor receptor (EGFR)-mutated lung adenocarcinoma. A 74-year-old female patient, who had remained disease-free for 14 years after undergoing right upper lobectomy for stage IA (pT1N0M0) lung adenocarcinoma, presented with headache and vomiting. Brain MRI demonstrated a 30 × 35 mm mass in the left parietal lobe with both solid and cystic portions abutting the dura and associated with surrounding edema, which was subsequently resected. Histopathological examination showed an admixture of meningioma and adenocarcinoma components, consistent with tumor-to-tumor metastasis. Immunohistochemistry revealed adenocarcinoma cells positive for thyroid transcription factor-1, Napsin A, and cytokeratin 7, supporting a pulmonary origin. Molecular testing identified an EGFR exon 19 deletion in both the intracranial lesion and the primary lung adenocarcinoma resected 14 years earlier, confirming a shared clonal origin. Following diagnosis, the patient received postoperative radiation therapy followed by osimertinib, and she remains recurrence-free three years after surgery. This case highlights an exceptionally rare pattern of recurrence, tumor-to-tumor metastasis of EGFR-mutated lung adenocarcinoma after right upper lobectomy into a meningioma, occurring 14 years after curative surgery. Oncologists should recognize that EGFR-mutated lung cancer can recur after an exceptionally long disease-free interval through rare metastatic patterns such as tumor-to-tumor metastasis.