If cancer is contained in the breast and the entire breast is removed and the lymph nodes are clear, why need adjutant therapy?

Depends. Not all need adjuvant chemo. There are some high risk factors we consider: grade 3, large tumor size, hormone receptor negative, her -2 positive, and/or high recurrence score (such as oncotype DX or mammaprint assay). These high risk features indicate a higher chance that some cancer cells have already travelled in the body. Adjuvant chemo is designed to get rid of these cancer cells.