Clinical behavior of advanced giant cell tumor: 15 years observation study in NN Blokhin National Medical Research Center of Oncology.

e23501 Background: Giant cell tumor of bone (GCT) is a relatively rare, benign but locally aggressive osteolytic skeletal neoplasm of young adults, most frequently occurs at the epiphysis of long bones. Distant metastases occur approximately 2-6% of cases most often to the lungs. However, pulmonary metastases do not carry the same connotation as metastases associated with malignant tumors, such as lung cancer or sarcoma. Rarely, GCT undergoes true malignant transformation. The aim of this study is to analyze the clinical behavior of advanced GCT during long-term observer in N.N. Blokhin National Medical Research Center of Oncology. Methods: We observed 51 advanced cases among 298 GCT from 2005 till 2020 in N.N. Blokhin National Medical Research Center of Oncology. Disease was histologically confirmed by a sarcoma pathologist. Patients underwent CT/MRI every 2 or 3 months of treatment and every 3, 6 or 12 months of follow up period. Treatment options were included atypical pulmonary resection, palliative surgery, chemotherapy with CAP or AI combination, interferon alfa or observation until progression. After 2013 prefer treatment option for advanced GCT was denosumab with once in 3 month’s regimen after 2 years monthly therapy. All patients received daily calcium and vitamin D supplement. Logistic regression was using for statistic analyzes. Results: Median follow-up was 45 months. The average age of patients was 34,8 years, and the women and men ratio was about 1,8:1. The most commonly affected sites were tibia (23,5%, 12/21), sacrum (17,6%), radius (13,7%) and femur (9,8%). According Campanacci classification G3 was the most commonly grade (90%). 46 (56%) cases were anatomically compounded due to tumor localization and 19 (37%) cases were primary disease. 18/298 (6%) cases were with pulmonary metastases. Surgery in history (p < 0,001) and tumor localization in extremity (p < 0,001) were significant for metastasis development. The primary malignant GCT observed in 1% (3/298) cases and 1 % cases of malignant transformation GCT into sarcoma. Only 1/51 (1,9%) death was observed in advanced GCT group. Complications ≥3 grade were observed only in pre-denosumab era. Conclusions: In this study we showed long-term observation of advanced GCT and evaluated significant factors for metastasis development. Surgeries in history and tumor localization were associated with higher risk of metastasis. Denosumab for advanced GCT is a choice of treatment, we wasn’t observed any cases of GCT malignant transformation during denosumab treatment. Quality of live was better in compare with pre-denosumab era. Further investigation of long term denosumab complications is awaited.