The FDA approves the groundbreaking drug trastuzumab (Herceptin) after research shows that adding the monoclonal antibody to chemotherapy dramatically increases survival for women with advanced breast cancer that over-produces a protein called HER2. In 2006, the drug is also approved as part of adjuvant therapy (after surgery) for women with early-stage HER2-positive breast cancer, after two major trials show that it reduces the risk of recurrence by more than 50 percent, an unprecedented result.

About 25 percent of breast cancer patients have HER2-positive disease, and prior to the introduction of trastuzumab, there were no effective treatments for these cancers, which were considered some of the most aggressive, deadly forms of the disease. Recently, trastuzumab was also FDA-approved to treat patients with stomach cancers that have a similar over-production of the HER2 protein.

An important study establishes a technique called sentinel lymph node biopsy as a standard part of breast cancer surgery. The procedure involves removing the lymph node closest to the primary tumor – the "sentinel" node – and examining it under a microscope for evidence of cancer. If the sentinel node is cancer-free, no further lymph nodes are removed and the patient is spared the previous practice of removing a large number of nodes and possibly larger sections of the breast. This more conservative approach allows for easier recovery and reduces the risk of postoperative side effects such as lymphedema, a painful swelling of the arm. If cancer is found, additional nearby lymph nodes are assessed, and often removed, and the patient is treated with additional chemotherapy after surgery. Recently, studies have shown that for some women, removing just the sentinel node may be sufficient.

Tamoxifen (Novaldex) is approved as adjuvant therapy for post-menopausal women following breast cancer surgery, based on studies showing that use of the hormonal therapy for five years after surgery reduces the risk of cancer recurrence and dramatically increases survival.

The first studies of the chemotherapy drug doxorubicin (Adriamycin) in breast cancer demonstrate that the drug can shrink breast tumors in women with advanced disease. Doxorubicin remains a mainstay of treatment for breast cancer today, often in combination with other drugs (such as cyclophosphamide, paclitaxel or docetaxel).