What is the definition or description of: plasmacytoma?

B cell neoplasm: There are cells in the bodies immune system that are known as B cells and otherwise known as plasmacytes. They produce antibodies that help fight infection. Cancers can develop in which B cells grow and reproduce without control. When these plasmacytes form a single tumor, it is called a plasmacytoma. When the cells form multiple lesion throughout the body the term is multiple myeloma.