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.