Dividing carcinoma cell, coloured transmission electron micrograph (TEM). A carcinoma is a malignant (cancerous) tumour caused by the uncontrollable proliferation of epithelial cells. Epithelial tissues in the human body include skin, glands and mucous membranes. This cell is undergoing mitosis (nuclear division), prior to dividing into 2 daughter cells. The nuclear membrane has dissolved and the chromosomes (red) have condensed and spread out along the centre of the cell in preparation for separation into their constituent chromatids. Magnification: x2400 when printed at 10 centimetres wide.