Which of the following is the most common primary bone tumor?

The most common primary bone tumor is multiple myeloma. This condition is characterized by the presence of malignant plasma cells in the bone marrow, leading to bone lesions and often resulting in pain, fractures, and other systemic symptoms. Multiple myeloma accounts for a significant portion of primary bone tumors and primarily affects older adults.

While osteosarcoma, Ewing sarcoma, and chondrosarcoma are indeed primary bone tumors, they are less commonly diagnosed compared to multiple myeloma. Osteosarcoma is more prevalent in adolescents and young adults and typically arises in long bones, while Ewing sarcoma primarily affects children and young adults and can arise in various bone locations. Chondrosarcoma arises from cartilage and is often seen in middle-aged adults, but it is also less common than multiple myeloma.

Thus, when considering the prevalence of primary bone tumors, multiple myeloma stands out as the most common, which supports its selection as the correct answer.