APBI: History, Rationale, and Controversies

Breast conservation for early-stage breast cancer is one of the remarkable achievements of modern cancer care. Numerous randomized clinical trials initiated >30 years ago have reported 20-year durable results documenting that survival is equivalent to mastectomy when the breast is conserved by removal of the index cancer with wide excision followed by whole-breast radiotherapy [1–4]. Since then, there has been extensive clinical research focused on optimizing the results of breast conservation in terms of defining the ideal patient population, surgical resection margins, role of systemic therapy, etc. Improvements in surgical and radiation methods as well as more effective systemic therapy agents have now resulted in equivalent local regional control for those undergoing breast conservation as compared to mastectomy in modern series [5, 6]. Nearly simultaneous to the initial trials studying breast conservation instead of mastectomy, investigators began to study alternative approaches that could achieve comparable cancer outcomes while reducing the burden of care imposed by the 4–6 weeks of daily radiotherapy delivery post lumpectomy (Fig. 1.1). Partial breast irradiation, that is, radiotherapy confined exclusively to the breast tissue adjacent to the surgical cavity, was among the earliest alternatives studied. This underscores the long history of partial-breast irradiation with roots of origin that extend nearly concurrent to the development of breast conservation itself. Multiple influences have since contributed to the development and success of what is now modern accelerated partial-breast irradiation (APBI) to make it one of many effective approaches available today for radiotherapy post lumpectomy in selected early-stage breast cancer patients.