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RARE-31. RECURRENT CHOROID PLEXUS CARCINOMA IN THE SETTING OF LI-FRAUMENI SYNDROME: REPORT OF TWO CHILDREN MANAGED WITH INTENSIVE RE-INDUCTION AND MARROW-ABLATIVE CONSOLIDATION CHEMOTHERAPY WITHOUT IRRADIATION FOLLOWED BY MOLECULARLY-TARGETED BIOLOGICAL THERAPY

Abstract BACKGROUND The optimal management for children with recurrent choroid plexus carcinoma (CPC), is not established. We report two children with germline TP53 mutations, whose CPC relapses were managed with marrow-ablative chemotherapy and oral biologically-targeted therapies. PATIENTS: Patient A: A 17 months old male presented with non-metastatic bilateral CPC. A de novo mosaic germline TP53 mutation was identified. After near-total resections, 16 months of standard chemotherapy were administered; 18 months later, localized tumor growth developed, again near-totally resected. Two cycles of re-induction chemotherapy were administered followed by three cycles of thiotepa/carboplatin with autologous hematopoietic cell rescue (AuHCR) and subsequently 21 months of sirolimus and thalidomide, continuing without residual or recurrent disease. Patient B: A 30 months old male presented with left lateral ventricular non-metastatic CPC. A de novo TP53 germline mutation was identified. Following sub-total resection, craniospinal irradiation with boost was administered followed by eight cycles of standard chemotherapy; 18 months later, localized recurrence developed; gross total resection was followed by 15 months of standard dose chemotherapies; four months thereafter, a second local recurrence developed, again gross totally resected. He then received one cycle of high-dose cyclophosphamide followed by three cycles of thiotepa/carboplatin with AuHCR. Subsequently he received sirolimus and thalidomide for 12 months, complicated by progressive pancytopenia. A small localized CPC recurrence was noted, gross totally resected, concomitant with myelodysplastic syndrome; he underwent an allogeneic matched unrelated donor marrow transplantation. CONCLUSIONS Marrow-ablative chemotherapy with post-transplant targeted biological therapy may afford durable survival for select children with recurrent CPC.

BACKGROUND: As genetic testing for both germline and tumor mutations has increased in completeness, complexity, and availability, more mutations and their impact on patient outcomes have been identified. METHODS: A retrospective review of pediatric patients who have identified germline mutations and a different tumor mutation was conducted. Data collected included demographics, tumor type, germline mutation status, tumor mutation status, relapse status, and patient outcome. RESULTS: Six patients aged 8-13 years old (median age 10 years) were identified for analysis. Four patients had pilocytic astrocytoma and two had pilomyxoid astrocytoma. One of the patients with pilocytic astrocytoma also had MPNST diagnosed very early at age 9. The combination of germline/tumor mutations is as follows: Neurofibromatosis Type I (NF1)/ BRAF v600e, NF1, CHEK2/MYB-QKI, NF1, Klinefelter, ATM, MUTYH, GPC3/BRAF-KIAA fusion, NF1/BRAF-KIAA (2 patients), and Marfan's/ BRAF-KIAA. The number of relapses per patient following initial diagnosis range from 3-7 with an average of 3.3. Four of the patients are alive and on therapy, which two are deceased. The two deceased patients both had NF1/ BRAF-KIAA fusions and pilocytic astrocytomas. CONCLUSIONS: Patients with differing and compounded germline and tumor molecular genetic mutations have worse outcomes. These patients have more relapses and death when compared to those patients with one mutation, either germline or tumor. Broad molecular testing and germline testing for mutations is crucial in determining patient risk for poor outcomes.

RARE-29. PRIMARY CENTRAL NERVOUS SYSTEM NON-HODGKIN LYMPHOMA IN AN 11-YEAR-OLD BOY: A CASE REPORT
Jorge Luis Ramírez-Melo 1 , Regina M Navarro-Martin del Campo 2,3 , Manuel D Martinez-Albarran 1 , Fernando Sánchez-Zubieta 4 , Ana L Orozco-Alvarado 2 , Luis A Arredondo-Navarro 5,3 , and Lorelai Gutierrez-Oliva 5 ; 1 Hospital Civil de Guadalajara "Dr. Juan I Menchaca", Guadalajara, Jalisco, Mexico, 2 Hospital Civil de Guadalajara "Dr. Juan I Menchaca", Guadalajara, Jalisco, Mexico, 3 GAPNO, INTERNATIONAL, Mexico, 4 Hospital Civil de Guadalara "Dr, Juan I Menchaca", Guadalajara, Jalisco, Mexico, 5 Hospital Civil de Guadalajara "Fray Antonio Alcalde", Guadalajara, Jalisco, Mexico BACKGROUND: Primary central nervous system lymphoma (PCNSL) are very rare in children. CLINICAL CASE: An 11-year-old male presented with a 2 months history with myoclonic movements in the upper right limb, and a sudden frontal headache, gait disturbance due to right hemiparesis and an ipsilateral convulsive episode. Upon admission he had critical condition, with hypertensive skull syndrome, Glasgow of 12, Karnofsky 40%, right hemiparesis, swallowing disorder, facial paralysis, and loss of photo motor reflex and unilateral amaurosis. A CT and MRI showed a huge tumor mass in the left tempo-parietal region, infiltrating the white matter and shifting the midline. A Tumor biopsy was done, and reported diffuse small cell non-Hodgkin lymphoma of high-grade, Burkitt type. Systemic lymphoma workup was negative. He received six cycles of chemotherapy based on high dose methotrexate, rituximab and triple intrathecal.After the second cycle an ophthalmologic evaluation was done, and found infiltration to the right retina, for which 6 cycles of intra vitreous chemotherapy with methotrexate were applied, he showed an excellent response, and recovered all his neurological functions except that right hemianopia persist. Control MRI showed partial response at 2 nd cycle and complete response after the 4 th cycle. No Radiation was performed. CONCLUSION: This report highlights the fact that pediatric PCNSL may be effectively treated by a combination of HDMTX and rituximab-based chemoimmunotherapy without irradiation. Lack of awareness of this rare entity may lead to extense resections of brain, and potential permanent secuelae that were avoided in this illustrative case.

RARE-30. A RARE CASE OF PRIMARY EWING'S SARCOMA OF THE CERVICAL SPINE
Amandeep Kalra 1,2 , Jayson Neil 2 , Sarah Mann 3 , and Pierre Giglio 4 ; 1 Sarah Cannon Cancer Institute, Kansas City, MO, USA, 2 HCA, Kansas City, MO, USA, 3 UC Davis, Sacramento, CA, USA, 4 Ohio State University, Columbus, OH, USA Ewing sarcoma family of tumors predominantly affect the pediatric population in the long bones of the extremities or the pelvis, and only 8% of cases arise within the spine. Primary Ewing's sarcoma of the cervical spine is extremely rare and less than 30 cases have been reported in the literature thus far. Here we present a case of primary Ewing's sarcoma of the cervical spine in a 28-year-old female who presented with a three-month history of neck pain and right arm radiculopathy. MRI revealed a homogeneously contrast enhancing, eccentric mass with dural tail at C2-C7. After undergoing a hemilaminectomy, histopathology confirmed extraosseous Ewing's sarcoma with CD99 positivity. A comprehensive systemic and neuraxis work-up ruled out overt metastasis. We extrapolated data from children's cooperative group studies and IESS-II clinical trial to formulate a three phase treatment protocol as described below. To date, patient is in remission with no evidence of any residual disease in the cervical spine. In conclusion, although Primary Ewing's sarcoma of the cervical spine is extremely rare it should be considered a differential diagnosis in patients with neck pain and a spinal mass under the age of thirty. Less than 25% of EFT's present with overt metastasis and almost all have subclinical metastatic disease at the time of diagnosis, therefore, a comprehensive evaluation and systemic chemotherapy is recommended. We recommend a multidisciplinary approach of surgical decompression to preserve neurological functions, followed by compressed chemotherapy regimens, reevaluation for local treatment, and adjuvant chemotherapy.
iii449 NEURO-ONCOLOGY • December 2020 TIENTS: Patient A: A 17 months old male presented with non-metastatic bilateral CPC. A de novo mosaic germline TP53 mutation was identified. After near-total resections, 16 months of standard chemotherapy were administered; 18 months later, localized tumor growth developed, again neartotally resected. Two cycles of re-induction chemotherapy were administered followed by three cycles of thiotepa/carboplatin with autologous hematopoietic cell rescue (AuHCR) and subsequently 21 months of sirolimus and thalidomide, continuing without residual or recurrent disease. Patient B: A 30 months old male presented with left lateral ventricular non-metastatic CPC. A de novo TP53 germline mutation was identified. Following subtotal resection, craniospinal irradiation with boost was administered followed by eight cycles of standard chemotherapy; 18 months later, localized recurrence developed; gross total resection was followed by 15 months of standard dose chemotherapies; four months thereafter, a second local recurrence developed, again gross totally resected. He then received one cycle of high-dose cyclophosphamide followed by three cycles of thiotepa/ carboplatin with AuHCR. Subsequently he received sirolimus and thalidomide for 12 months, complicated by progressive pancytopenia. A small localized CPC recurrence was noted, gross totally resected, concomitant with myelodysplastic syndrome; he underwent an allogeneic matched unrelated donor marrow transplantation. CONCLUSIONS: Marrow-ablative chemotherapy with post-transplant targeted biological therapy may afford durable survival for select children with recurrent CPC.

RARE-32. PEDIATRIC METASTATIC SKULL BASE CHORDOMA WITH TP53 MUTATION -A CASE REPORT AND REVIEW OF THE LITERATURE
Akira Shimada 1 , Kazuhiko Kurozumi 1 , Kiichiro Kanamitsu 1 , Hisashi Ishida Ishida 1 , Kaori Fujiwara 1 , Kana Washio Washio 1 , Tadashi Kumamoto 2 , Chitose Ogawa 2 , and Masahiro Shin 3 ; 1 Okayama University Hospital, Okayama, Japan, 2 National Cancer Center, Tokyo, Japan, 3 Tokyo University, Tokyo, Japan Chordoma is an uncommon bone tumor arising from notochordal remnant, which accounts for 1-4% of all bone malignancies. It commonly occurs along the cranial-spinal axis, and skull base is one of most frequent sites, representing 35-49% of all chordoma cases. Surgical resection is widely accepted as the first choice of treatment. There are only limited number of reports about pediatric chordoma cases, and its biological behavior including genetic backgrounds were largely unknown. Here, we present a 5 year-old girl with a large aggressive skull base chordoma of 6 cm in maximum diameter, which eventually had multiple systemic metastasis. We initially tried chemotherapy based on the protocol for the osteosarcoma, but in vain. Because the tumor was highly vascularized on angiography, after embolization of the feeding arteries and bilateral internal maxillary arteries, endoscopic endonasal surgery was performed. The tumor was sufficiently removed, achieving effective mass reduction, and the residual tumors involving the lower cranial nerves and craniocervial junction were additionally treated with Gamma Knife radiosurgery. However, one month later, it showed systemic metastasis to bilateral cervical lymph nodes and lung. We tried chemotherapy with nivolmab and imatinib for this patient, whereas they showed the partial effect. The genetic analysis revealed somatic TP53 c.569C>T, (p.P190L) mutation in chordoma specimen. In the past literature, we found only one study of the adult chordoma cases, in which majority of the patients had somatic TP53 mutation (p.P72R). Further investigation with large number of the cases is essential to clarify the molecular biology of pediatric chordomas.

RARE-33. GIANT CELL TUMOR OF THE SKULL BASE WITH A HISTORY OF A SUCCESSFUL RESPONSE TO DENOSUMAB AND LATER DEVELOPING A SECOND TUMOR
Manushak Avagyan 1,2 , Gevorg Tamamyan 1 , Samvel Danielyan 1 , Martin Harutyunyan 2 , Nune Karapetyan 3 , Nerses Karamyan 4 , Hovhannes Vardevanyan 5 , Armen Mkhitaryan 6 , and Samvel Bardakhchyan 1 ; 1 Hematology Center After Prof. Yeolyan, Yerevan, Armenia, 2 Yerevan State Medical University, Yerevan, Armenia, 3 Yerevan, Yerevan, Armenia, 4 "IRA Medical Group" Radiotherapy Center, Yerevan, Armenia, 5 Armenian-American wellness center, Yerevan, Armenia, 6 "Histogen" Armenian-German Scientific Practical Center of Pathology, Yerevan, Armenia BACKGROUND: Giant cell tumor of bone(GCTB) is a rare neoplasm with unpredictable behavior, possible malignant transformations, and/or lung metastases. Surgery is usually the treatment of choice. In unresectable or metastatic cases, treatment with denosumab is a new treatment option. CASE PRESENTATION: A 14-years-old female presented with cachexia, dysphagia, diplopia, discoordination, strabismus, and multiple cranial nerve palsies in 10.2015. MRI revealed intra-extracranial mass arising from C2 vertebrae, compressing the medulla oblongata and the left cerebellar hemisphere, invading to the sphenoid bone and nasopharynges. Biopsy showed a GCTB. Surgical resection was done, which was incomplete because of tumor location (cranial nerve and vertebral artery involvement). Then local radiation therapy was performed 50.4Gy. During RT patient's condition declined and MRI showed disease progression. Treatment with denosumab 120mg q4w was initiated in 03.2016, which yielded successful results. Disease was under control for three years until 03.2019. Then she returned with clinical symptoms of diplopia and severe headache. MRI showed local tumor progression. Repeated biopsy revealed undifferentiated pleomorphic sarcoma, which could be either a malignant transformation of GCTB or a new tumor. The patient later underwent two cycles of chemotherapy with Ifosfamide/Doxorubicin. MRI after 2nd cycle showed marked tumor progression. The patient didn't receive any further treatment because of cachexia and died due to disease progression in 12.2019. CONCLUSION: To our knowledge, this is the youngest patient ever reported with a skull base tumor with such a clinical development, successful and long-time remission with denosumab and with such a chemotherapy-resistant malignant transformation or second cancer.