(P 028) LONG TERM SURVIVAL OF AN ANTERIOR SKULL BASE OSTEOSARCOMA ARISING FROM FIBROUS DYSPLASIA TREATED WITH TRIMODALITY THERAPY

Objective: Sarcomatous change of monostotic fibrous dysplasia (FD) is rare, occurring in less than 1%. Osteosarcoma is the major histologic type of malignant transformation of FD, followed by fibrosarcoma, chondrosarcoma, and malignant fibrous histiocytoma, with most cases reported years after radiation treatments. Here we report a case, not involving previous radiation, of a 5+-year survivor originally diagnosed with an osteoblastic osteosarcoma in the anterior skull base arising from fibrous dysplasia, treated with surgery, standard of care chemotherapy and then high dose proton beam radiation.

Methods: In late 2015, a 28-year-old man noted onset of nasal symptoms. By December 2015, he developed onset of facial pain and an egg-shaped lesion of the right parietotemporal region. The patient sought medical attention on 12/28/2015. He was noted to have facial dysmorphia due to fibrous dysplasia and a mass of the right temporal region.
MRI axial T2 FLAIR images 1/6/2016 showed craniofacial fibrous dysplasia with a superimposed focal cystic and solid right lateral frontal calvarial and sphenoid wing mass suggestive of sarcomatous degeneration (Image 1A).
The patient was admitted and taken to OR for right orbital craniotomy with resection of this extradural tumor involving the anterior skull base, extending to the clivus. Post-op MRI on 1/8/2016 is shown in Image 1B.
Between our pathology team and a second opinion from Dr. Andrew Rosenberg in Miami, FL, we arrived at a diagnosis of osteoblastic osteosarcoma, grade 3, arising in an area of fibrous dysplasia.  
Staging indicated localized disease, so the patient proceeded to standard chemotherapy with adriamycin, cisplatin, and high-dose methotrexate (MAP).
Due to anatomical location and subsequent concerns for local recurrence, he was then referred to Dr. Daniel Hamstra in Dallas, TX for proton beam radiation therapy.  He completed 76 Gy with Intensity-Modulated Proton Therapy in October 2016.

Results: Over the Spring of 2019, he started having debilitating headaches. Changes seen on MRI June 2019 were consistent with post-radiation necrosis (Image 2A). He was started on steroids with relief of symptoms, and improvement in imaging characteristics.
He was started on monthly Zometa early 2019 for his underlying fibrous dysplasia and finished 24 months of such in Spring 2021.
Latest surveillance MRI head May 2022 (Image 2B) was showing ongoing improvement in radiation necrosis changes, most pronounced in frontal lobes, as well as no signs of local recurrence along right calvarium.
He is working full time and coaching his child's soccer team. Since all of his treatment, he has also been able to have children naturally with his wife.

Conclusion: This young man was treated with trimodality therapy for an osteoblastic osteosarcoma in the anterior skull base arising from fibrous dysplasia. Due to challenging anatomical location, we used high dose proton beam radiation for local control, after surgery and standard chemo were completed. This presentation also shows the necessity of multi-institution care with challenging cases like his. He is now five-plus years out from completion of therapy and living life to the fullest.
**Special thanks to Andrew Rosenberg, MD and Daniel Hamstra, MD, PhD