A Brain Metastasis in Search of Its Origin: Occult Primary Non-small Cell Lung Cancer

We present a case of a 67-year-old man who presented with right-sided hemiparesis and headache and was found to have a solitary left temporoparietal cerebral lesion on MRI, initially favoring a primary brain tumor.Further workup was unremarkable and the patient underwent surgical resection of the cerebral lesion.Histopathology and immunohistochemistry favored a metastatic pulmonary adenocarcinoma, though imaging scans showed no primary lung lesion.Subsequent PET-CT demonstrated hypermetabolic mediastinal, hilar, and supraclavicular lymphadenopathy, consistent with occult primary non-small cell lung cancer.The patient underwent stereotactic gamma knife radiotherapy to the resection bed, followed by systemic chemotherapy with cisplatin and vinorelbine.At the time of writing, two of three planned chemotherapy cycles had been completed, with radiological response assessment scheduled after completion of the treatment.This case adds to the limited literature on occult primary non-small cell lung cancer (NSCLC) and supports early tissue diagnosis as key to appropriate management.