SUN-512 Novel Germline TMEM127 Mutation in a Patient with Pheochromocytoma and Breast cancer

Abstract Disclosure: I. Jochmanova: None. The coincidence of synchronous pheochromocytoma and breast cancer is a rare condition. Here, we present a case of a 51-year-old female with a history of arterial hypertension and hypercholesterolemia who was diagnosed with HER2-positive invasive ductal right breast carcinoma and concomitant left adrenal lesion (32x29x31 mm) on a CT scan. Plasma metanephrines were not elevated at the time of diagnosis, so the lesion was thought to be a breast carcinoma metastasis, although metastatic spread of breast carcinoma to the adrenal glands is very rare. Family history was significant for breast cancer in the patient’s second sister, and thus, genetic testing for hereditary tumor syndromes was performed. This was negative for hereditary breast and ovary cancer syndromes, however, a pathogenic, not yet published, germline TMEM127 (c.600del, p.Thr201GInfs*106) variant was found. Eighteen months later, after neoadjuvant chemotherapy and a bilateral mastectomy for breast cancer, the patient underwent a left adrenalectomy, and histological evaluation confirmed pheochromocytoma. Postsurgical plasma metanephrines were within normal limits and the CT scan did not reveal any other lesions; 68Ga-DOTA TATE PET/CT results are pending. The patient is currently doing well on aromatase inhibitor treatment for her breast carcinoma. So far, only three cases of breast cancer and pheochromocytoma have been published, none of them in a patient with TMEM127 mutation. TMEM127 alterations are present in around 0.36% of all cancers, including breast invasive ductal carcinoma and pheochromocytoma. However, the exact relationship between these two tumors is not entirely understood yet. In patients with confirmed pathogenic mutations in cancer-predisposing genes, a thorough evaluation, multi-disciplinary approach, appropriate treatment of each tumor entity, and regular follow-up are needed. Presentation: Sunday, July 13, 2025