Pituitary gland metastasis is an uncommon situation seen in advanced stages of malignancies. The diagnosis of advanced cancer with pituitary metastasis is a rarer presentation. Lung and breast cancers are the most common form of primary malignancies that metastasize to the pituitary gland. Mucinous adenocarcinoma is a rare histological subtype of breast cancer. Here, we report a case of a patient diagnosed with pituitary gland metastasis who had a long survival achieved by a multimodality treatment approach. The patient was diagnosed with the excisional biopsy of a pituitary gland lesion. After a partial response to chemotherapy, letrozole treatment was initiated. After eight years, a recurrent lesion was determined in her right breast. She underwent a right modified radical mastectomy and axillary dissection and letrozole treatment was continued. Follow-up and treatment are still ongoing. In this case, multimodal treatment was effective in achieving long-term survival. Thus, metastasis should be considered in the differential diagnosis of pituitary lesions.