Neoadjuvant therapy is treatment given before surgery and most commonly considered for high risk and /or locally advanced breast cancers (stage II or III cancers). Neoadjuvant therapy can include different therapies. For example, you may get chemotherapy before your surgery to help shrink the tumour.

It is rare for radiation to be given prior to surgery in a neoadjuvant setting for a large and unresponsive tumour.

Adjuvant therapy is a treatment given after and in addition to surgery and help lowers the risk of your breast cancer coming back. Adjuvant therapy includes chemotherapy, radiation therapy and hormone therapy as well as targeted biological therapies. For example, your doctor may give you radiation therapy after you've had your surgery to make sure any remaining cancer cells within your breast are eliminated.

While your surgery to remove the cancer may have been successful, there is no way of guaranteeing that the cancer is completely gone. For this reason, adjuvant therapy is often given to decrease the risk of recurrence.

The goal of treatment for early stage breast cancer is to get rid of the cancer completely. To do this, doctors will usually recommend surgery and treatment after surgery (adjuvant). Some patients may also receive treatment prior to surgery (neoadjuvant therapy).

 
While your surgery to remove the cancer may have been successful, there is no way of guaranteeing that the cancer is completely gone. Some of the cancer cells may not be detectable when the primary tumour is surgically removed. If these cells are not cleared sufficiently through treatment, they can contribute to the disease returning and spreading. For this reason, adjuvant therapy is often given to decrease the risk of recurrence.
 
In many cases, early stage breast cancers can be treated successfully by surgery alone. Over time however, adjuvant treatment has been seen as the gold standard for breast cancer treatment.