A 62-year-old woman with multiple sclerosis and no history of malignancy, incidentally presented with a diffusely enlarged and homogeneously enhancing pituitary gland associated with stalk enlargement. The clinical and biochemical evaluation revealed anterior hypopituitarism and diabetes insipidus. Hypophysitis was considered the most likely diagnosis. However, rapid visual deterioration and pituitary growth raised the suspicion of metastatic involvement. A search for systemic malignancy was performed, and CT revealed a lung mass, which proved to be a lung adenocarcinoma. Accordingly, the patient was started on immunotherapy. Resection of the pituitary lesion was performed, and histopathology analysis revealed metastatic lung adenocarcinoma. Following surgery, the patient underwent radiotherapy. More than 2 years after PM detection, the patient shows a clinically relevant response to antineoplastic therapy and no evidence of PM recurrence ¹⁾.