Background/Aim: Primary bone neoplasms include osteosarcomas (OS), chondrosarcomas (CS), and giant cell tumors (GCT). Nicotinamide phosphoribosyl transferase (NAMPT) catalyzes the rate-limiting step of nicotinamide adenine dinucleotide synthesis and is increased in multiple tumor types. In malignancies, NAMPT expression often correlates positively with tumor grade, chemotherapy resistance, and metastatic potential. Materials and Methods: Tissue microarray was used to examine NAMPT expression in benign bone and cartilage, GCTs, OS, and different CS grades. Results: For the first time, we showed that NAMPT expression was increased in GCTs and OS compared to benign bone, and in CS compared to benign cartilage. Its expression also increased with higher CS grade. Conclusion: Our data indicate that NAMPT plays a role in bone sarcomas and GCTs, and its higher expression may contribute to increased tumor aggressiveness. Malignancies of the bones and joints are rare, comprising 0.2% of all human neoplasms. In the United States, approximately 3,450 were diagnosed in 2017, while in the same year these malignancies caused 1,590 deaths (1, 2). Among these malignancies, osteosarcomas (OS) and chondrosarcomas (CS) constitute 36% and 20-25% of bone and joint malignancies, respectively (1-3). While OS can occur in patients of all ages, it exhibits a bimodal distribution, with disease peaks at 15-19 years and 75-79 years (1-3). Although most cases are sporadic, factors such as radiation exposure, Paget's disease of the bone, and genetic susceptibilities increase OS risk (1-4). They commonly present in the long bones at areas of rapid bone growth, typically adjacent to the metaphyseal growth plate, commonly at the proximal humerus and tibia, and distal femur (1-4). OS is more common in males and confers different survival rates by different ages and anatomic locations (1-4). In adolescents and children, the 5-year survival rate is approximately 55-75%, with older individuals having an approximately 57% 5year survival rate that falls with increasing age (1-4). Histologically, OS exhibit malignant pleomorphic cells with an osteogenic differentiation that produces osteoid, typically in irregular trabeculae (1-4). While malignant bone is always present, the matrix of conventional OS may have chondroid, fibroblastic, or cartilaginous features (1-4). Less common OS subtypes include telangiectatic, small-cell, periosteal, paraosteal, extraskeletal, and secondary OS (1-4). CS are adult bone sarcomas and often present as slowgrowing heterogenous malignancies in individuals between 30 and 60 years old (2-3, 5). CS are associated with a 5-year survival rate of approximately 70%, are slightly more common in males, and commonly occur in the lower limbs, pelvis, sternum, ribs, and clavicle (2-3, 5). CS is often graded on a I-III scale, with 90% graded I-II and 5-10% grade III, which carry significant metastatic potential (2-3, 5). CS is classified as primary if not associated with a preexisting chondroid lesion and secondary if they it is, often...

Plasmablastic lymphoma (PBL) is an aggressive malignancy that usually occurs in the setting of immunosuppression. The immunohistochemical profile of PBL is that of terminally differentiated B lymphocytes. CD138, CD38, and MUM1 are usually immunopositive. However, pan B-cell markers such as CD20 and PAX-5 are usually negative.MYCrearrangement is the most commonly encountered genetic alteration, with immunoglobulin (IG), especially immunoglobulin heavy (IGH) chain, being the most frequent partner. We report a case of PBL in a 48-year-old human immunodeficiency virus- (HIV-) positive male who was admitted to the hospital with signs and symptoms suspicious for tumor lysis syndrome. Bone marrow examination revealed hypercellular marrow with trilineage hypoplasia and sheets of intermediate to large neoplastic cells with basophilic vacuolated cytoplasm comprising the majority of cellular elements of the bone marrow. The neoplastic cells were negative for conventional B-cell, T-cell, plasma cell, and myeloid markers, while flow cytometric analysis revealed an abnormal CD45-dim population that was partially weakly positive for CD71 and CD79b. The diagnosis was initially thought to be a high-grade primitive hematopoietic neoplasm, possibly an acute undifferentiated leukemia. BOB-1, however, was immunopositive in the neoplastic cells, confirming its B-cell origin. MYC was positive by immunohistochemistry and break-apart FISH, as were CD45, MUM-1, and EMA immunostains. There was immunoglobulin kappa (IGK) light chain gene rearrangement by polymerase chain reaction (PCR). Additionally, Epstein–Barr virus- (EBV–) encoded small RNAs (EBER) were positive by in situ hybridization (ISH). The tumor proliferation index by Ki-67 immunostaining approached 95%. Although the tumor cells were negative for CD38 and CD138, the diagnosis of PBL was still rendered. We recommend using a broad spectrum of B-cell markers, including BOB-1 and OCT-2, in such challenging cases of B-cell lymphomas with no expression of conventional B-cell markers. We also emphasize that the negative CD38 and CD138 should not exclude PBL from the differential diagnosis.

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