Plasma cell neoplasms are a group of disorders characterized by the abnormal growth of plasma cells, which are a type of white blood cell responsible for producing antibodies. The most common type is multiple myeloma, where malignant plasma cells accumulate in the bone marrow, leading to various health issues, including bone pain, anemia, and kidney problems. Other forms of plasma cell neoplasms include plasmacytoma, which is a localized tumor of plasma cells, and Waldenström macroglobulinemia, a condition that involves high levels of a specific type of antibody. Diagnosis typically involves blood tests, imaging studies, and bone marrow biopsies to assess the extent of the disease.