Plasmacytoma. Coloured transmission electron micrograph (TEM) of malignant cancer cells in a plasmacytoma, a tumour of plasma cells. The large, irregular nuclei in these cells indicate they are actively dividing. Both factors, irregular nuclei and proliferation, are characteristic of cancerous cell. The cell in the middle is undergoing mitosis (division of the nucleus). Its nuclear membrane has disappeared and the chromosomes (red) are about to divide into two identical sets. Mitosis is a prelude to cell division. Plasma cells are a type of white blood cell found in bone marrow. Magnification x2225 at 6x4.5cm size.