Milestones in breast cancer treatment.

Modern treatment started in the 1880s with Halsted's mastectomy. The next milestone-a century later-was breast-conserving surgery, with equivalent survival but better esthetic outcomes than mastectomy. Sentinel node biopsy, introduced in the 1990s, was a milestone that permitted avoidance of axillary dissection if the sentinel node was disease-free. Chemotherapy was established for early breast cancer in the 1980s and its efficacy continues to improve; however side effects remain a concern, particularly since chemotherapy does not benefit most patients. External whole breast irradiation was introduced with conservative surgery, as it reduces recurrences. By the 2000s, 3-week regimens had been shown equivalent to standard 6-week regimens-easing pressure on patients and radiation centers. Intraoperative partial breast irradiation is potentially more beneficial as it permits complete local treatment in a single session; however, trials show that patients must be very carefully selected. From the 1990s irradiation technology was combined with imaging and computer technologies to produce equipment that directs radiation to more precisely defined target volumes, allowing increased dose to the target and markedly reduced dose to nearby tissues. Irradiation systems are evolving rapidly but are being implemented without data on long-term morbidity or efficacy, while costs rise steeply. The first targeted treatment was tamoxifen, a selective estrogen receptor inhibitor. Since its widespread use starting in the 1980s, tamoxifen has saved the lives or prolonged the survival of millions with estrogen-positive disease; it is cheap and has limited (but not negligible) side effects. The same cannot be said of newer targeted treatments like trastuzumab and pertuzumab, which, although effective against human epidermal growth factor receptor 2-positive cancer, come with important side effects and huge costs. Breast cancer mortality is declining in rich countries, but treatments have become more demanding and more expensive, so the outlook for the increasing numbers of women worldwide who develop the disease is uncertain.