What is breast cancer?

Did you know that breast tissue covers an area larger than just the breasts? Since breasts sit on the chest muscles that cover the ribs, they actually extend all the way to the collarbone and from the centre of your chest to the armpits.

Illustration of the breast and surrounding structures

Breast cancer is a disease that develops when abnormal cells multiply in the breast tissue. Normally, breast tissue cells grow, work, reproduce and die in an orderly way. But cancer cells multiply in an uncontrolled way, creating a lump, or tumour. If the tumour isn’t treated, it may spread and damage or destroy healthy tissue around it. Eventually, it can be life-threatening.

Not all abnormal cell growth in the breast area is harmful. Tumours that test negative for cancer are benign, meaning they don’t spread to other parts of the body and are not life threatening.