SUN-714 McCune-Albright Syndrome: A Case of an Adult With Fibrous Dysplasia, Severe Cardiopulmonary Complications, Acromegaly and Chronic Myeloid Leukemia

Abstract Disclosure: A.J. Ji: None. A. Mclean: None. A.K. Sinha: None. McCune-Albright syndrome (MAS) is a rare mosaic disorder characterized by the classic triad of fibrous dysplasia of bone (FD), café-au lait skin macules and hyperfunctioning endocrinopathies. MAS is caused by a postzygotic mutation in the guanine nucleotide stimulatory protein gene. There is no approved treatment for MAS.We present the case of a 43-year-old male carpenter with severe polyostotic FD and adult-onset growth hormone excess who was treated with denosumab and somatostatin analogue, complicated with a diagnosis of chronic myeloid leukemia (CML). The patient had a medical history of polyostotic FD since his childhood that was managed in his home country. Pituitary screening performed until the age of 18 showed no evidence of hyperfunctioning endocrinopathies. Multiple skeletal sites were involved including his lower limbs, left clavicle, left thoracic cage, and craniofacial bones. These resulted in complications of a severe restrictive ventilatory defect from the left thoracic cage deformity, dilated cardiomyopathy and compression of the left superior vena cava and the internal jugular vein. His main symptoms were dyspnea on exertion, severe pain around the left clavicle in the context of physically demanding carpentry work. The investigations at the initial endocrinology assessment showed alkaline phosphatase of 466U/L (30-11U/L), and an elevated C-terminal telopeptide of type 1 collagen of 2590ng/L (100-600ng/L). MRI of his left shoulder demonstrated a marked expansile mass with a maximum diameter of 9.3cm. Biopsy of the left clavicle lesion showed no malignant cells on histopathology. A forequarter amputation was considered to treat a large clavicular lesion, however, involvement of his thoracic cage resulted in significant cardiopulmonary impairment including restrictive lung disease and the surgery was deemed too risky. Denosumab was commenced after failed zoledronic acid for pain management resulting alleviation of pain. Screening of endocrinopathy revealed growth hormone excess with an elevated IGF-1 level and 7mm pituitary adenoma. Lanreotide was commenced as a medical therapy resulting reduction in IGF-1 levels. Over 9 months into the denosumab treatment, the patient was diagnosed with CML in the context of a routine full blood examination. The patient achieved a hematological remission with imatinib. Polyostotic FD can lead to serious of complications from severe deformities of the skeleton, including cardiopulmonary complications. This is the first case of a patient with MAS/FD reported with a diagnosis of CML, although it is unlikely due to the MAS as the two have different pathogenic pathways. Denosumab is effective in pain management however, should be used with a caution and there are no large studies to guide long term management. Evaluation and management of MAS should also include detailed endocrinopathy assessment and screening even in adulthood. Presentation: Sunday, July 13, 2025