Plasmacytoma is a type of tumor that arises from plasma cells, which are a kind of white blood cell responsible for producing antibodies. It can occur in various parts of the body, most commonly in the bone or soft tissues. When it occurs in the bone, it is often referred to as solitary plasmacytoma, while multiple plasmacytomas can indicate a more widespread condition known as multiple myeloma. Diagnosis typically involves imaging tests, such as X-rays or MRIs, and a biopsy to confirm the presence of abnormal plasma cells. Treatment options may include radiation therapy, chemotherapy, or stem cell transplants, depending on the severity and location of the tumor.