Breast cancer cell. False-colour scanning electron micrograph (SEM) of a single breast cancer cell, showing its uneven surface and cytoplasmic projections. Clumps of cancerous (malignant) cells form tumours, which possess the ability to invade & destroy surrounding tissues & travel to distant parts of the body to seed secondary tumours. Malignant cells proliferate & grow in a chaotic manner, with defective cell division retained within each new generation of cells. Variations also occur in size and structure, from close resemblance to original cell type (well differentiated) to complete undifferentiation.