Confocal light micrograph of MCF-7 human breast carcinoma cells that have been grown in a mouse. Fluorescent markers have been used to highlight structures in the cell. DNA (deoxyribonucleic acid) in the cells' nuclei is red. Alpha tubulin, a component of microtubules, is blue. Microtubules are components of a cell's cytoskeleton. The cytoskeleton maintains the cell's shape, allows some cellular mobility and is involved in intracellular transport and nuclear division. MCF-7 are hormone-responsive cells used to study the metastasis (spread) of breast cancer.