**4.3 Ductal carcinoma in situ**

It is the most common type of non-invasive breast cancer, because it only affects the breast duct. Ductal comedocarcinoma is an example of ductal carcinoma *in situ*.

## **4.4 Invasive breast cancer**

When abnormal cells from the lobules or milk ducts break off and come into contact with breast tissue, this condition occurs. Through the immune system or the systemic circulation, cancer cells may spread from the breast to other areas of the body. They may migrate early in the formation of the tumour, when it is small, or later, when it is large. Invasive breast cancer is the most common kind of cancer in women. Metastatic breast cancer is defined as invasive breast cancer that has spread to other parts of the body. The brain, bones, lungs, and liver are the most frequent organs to which these cells travel. These cells separate and grow irregularly once again, resulting in new tumours. Although new forming cells are appearing in many parts of the body,but still remains to be breast cancer cells [9, 10].
