Giant cell tumor (GCT) of bone is one type of giant cell-rich lesion of bone. This benign mesenchymal tumor has characteristic multinuclear giant cells. Mononuclear stromal cells are the physiologically active and diagnostic cell type. Most GCTs are located in the epiphyseal regions of long bones. The axial skeleton-primarily the sacrum-is a secondary site of involvement. Most patients present with pain, swelling, joint effusion, and disability in the third and fourth decades of life. Imaging studies are important for tumor staging and radiographic grading. Typically, these clinically active but slow-growing tumors are confined to bone, with relatively well-defined radiographic borders. Monostotic disease is most common. Metastatic spread to the lungs is rare. Extended intralesional curettage with or without adjuvant therapy is the primary treatment choice. Local recurrence is seen in ≤ 20% of cases, and a second local intralesional procedure is typically sufficient in cases that are detected early. Medical therapies include diphosphonates and denosumab. Denosumab has been approved for use in osteoporosis as well as breast and prostate cancer metastatic to bone. Medical therapy and radiotherapy can alter the management of GCT of bone, especially in multifocal disease, local recurrences, and bulky central/axial disease.

The recent impressive clinical responses to antibody-based immunotherapy have prompted the identification of clinically relevant tumor antigens that can serve as targets in solid tumors. Among them, B7-H3, a member of the B7 ligand family, represents an attractive target for antibody-based immunotherapy, it is overexpressed on differentiated malignant cells and cancer-initiating cells, with limited heterogeneity, and high frequency (60% of 25,000 tumor samples) in many different cancer types, but has a limited expression at low level in normal tissues. In nonmalignant tissues, B7-H3 has a predominantly inhibitory role in adaptive immunity, suppressing T-cell activation and proliferation. In malignant tissues, B7-H3 inhibits tumor antigen–specific immune responses, leading to a protumorigenic effect. B7-H3 also has nonimmunologic protumorigenic functions, such as promoting migration and invasion, angiogenesis, chemoresistance, and endothelial-to-mesenchymal transition, as well as affecting tumor cell metabolism. As a result, B7-H3 expression in tumors is associated with poor prognosis. Although experimental B7-H3 silencing reduces cancer cell malignant potential, there has been limited emphasis on the development of B7-H3–blocking antibodies, most likely because the B7-H3 receptor remains unknown. Instead, many antibody-based strategies utilizing distinct effector mechanisms to target B7-H3–expressing cancer cells have been developed. These strategies have demonstrated potent antitumor activity and acceptable safety profiles in preclinical models. Ongoing clinical trials are assessing their safety and efficacy in patients. Identification of the B7-H3 receptor will improve our understanding of its role in tumor immunity, and will suggest rational strategies to develop blocking antibodies, which may enhance the therapeutic efficacy of tumor immunity.

Programmed cell death 1 ligand 1 (PD-L1, B7H1) is a cell-surface protein that suppresses the cytotoxic CD8+ T cell-mediated immune response. PD-L1 expression and its clinical relevance in sarcomas are not well understood. Therefore, we sought to measure RNA expression levels for PD-L1 in 38 clinically annotated osteosarcoma tumor samples, and aimed to determine if PD-L1 expression correlates with clinical features and tumor-infiltrating T-lymphocytes (TILs). Quantitative real-time RT-PCR for PD-L1 was optimized in 18 cell lines, of which 5 were osteosarcoma-derived. qRT-PCR results were validated via flow cytometry and immunohistochemistry (IHC) in select cell lines. Total RNA was isolated from 38 human osteosarcoma samples for qRT-PCR analysis. Clinical data were sorted and significance was determined by Student t-test. TILs were examined in patient samples by tissue microarray (TMA) hematoxylin-eosin (HE) staining. We confirmed the constitutive PD-L1 mRNA expression in cell lines by qRT-PCR, flow cytometry, and IHC. Across human osteosarcoma samples, PD-L1 mRNA gene expression ranged over four-log (>5000-fold difference). Relative expression levels were evaluated against clinical factors such as age/gender, metastasis, recurrence, chemotherapy, percent necrosis, and survival; no significant associations were identified. The presence of TILs was associated with high PD-L1 expression (R2=0.37, P=0.01). In summary, we developed an RNA-based assay to determine PD-L1 expression levels, and we show for the first time that high levels of PD-L1 are expressed in a subset of osteosarcoma, and PD-L1 expression is positively correlated with TILs. There are multiple agents targeting PD-1/PD-L1 in clinical development, and this may be a novel immunotherapeutic strategy for osteosarcoma clinical trials.

LC with this treatment is high in patients with primary tumors. Late morbidity appears to be acceptable.