Breast cancer usually begins in the milk ducts or in the milk-producing lobules. For a long time the abnormal cells stay contained — this is called carcinoma in situ. When they cross the duct or lobule wall into the surrounding breast tissue, the cancer becomes invasive.
The stages of development
- A single cell undergoes changes (mutations) in its DNA
- The changed cell divides faster than its neighbours
- The cells form a contained cluster (carcinoma in situ)
- Without intervention, the cells invade nearby tissue (invasive cancer)
- Cells can travel through the lymph or blood to other organs (metastasis)
Not all cancers grow at the same speed. Some develop over many years, others more quickly. That is why the earlier a change is detected, the better — we can act while the cancer is still small and localised.