Which cancer type is marked by the excess growth of plasma cells?

The cancer type characterized by the excess growth of plasma cells is multiple myeloma. In this condition, there is an abnormal proliferation of plasma cells, which are a type of white blood cell that produces antibodies. When these cells become malignant, they proliferate uncontrollably, leading to a range of complications, including destructive bone lesions and the production of abnormal proteins.

In the context of the other options, while hematopoietic neoplasm broadly encompasses cancers arising from blood-forming tissues, it includes a variety of diseases, not specific to the overgrowth of plasma cells. Melanoma, on the other hand, refers specifically to skin cancer originating from melanocytes, and lymphosarcoma, or lymphoma, pertains to cancers of the lymphatic tissue, which primarily affect lymphocytes, not plasma cells. Thus, the defining feature of multiple myeloma’s excess plasma cell growth distinctly identifies it among the listed options.