Immunofluorescent Light Micrograph of cancer cells of the human breast. Cultured in the laboratory, these cancer cells have formed a dense single layer (confluent monolayer). Such malignant cells typically are large and undifferentiated, with a capacity to divide rapidly. The prominent nucleus of each cell stains blue; cytoplasm is red; cell membranes are yellow. At upper frame, mitotic cell division can be seen in cells containing a small cytoplasm. Immunofluorescence is a staining tech- nique which uses antibodies to attach fluorescent dyes to specific tissues and to molecules within the cell. Magnification: x200 at 35mm size.