Breast Cancer Outcomes of Neoadjuvant Versus Adjuvant Chemotherapy by Receptor Subtype: A Scoping Review

Trials demonstrate equivalent survival for breast cancers treated with neoadjuvant chemotherapy (NAC) or adjuvant chemotherapy (AC). However, these were conducted before the recognition of the importance of receptor subtype for survival and chemotherapy response. Therefore, chemotherapy timing may impact survival for certain receptor subtypes. A scoping review of studies assessing outcomes by chemotherapy timing based on receptor subtype was conducted to evaluate gaps in the existing literature. Three databases were searched in February 2019 with terms related to breast cancer, NAC/AC, and survival. Inclusion criteria were original peer-reviewed studies published in English after 1989 comparing breast cancer outcomes for females based on chemotherapy timing. Studies/sections of studies lacking outcomes by receptor subtype or including patients missing appropriate targeted therapy were excluded. Of 7354 articles, 262 abstracts and 60 full texts were reviewed. Three studies met criteria. All were single-institution retrospective studies analyzing outcomes for triple negative (TN) patients with one study also examining luminal A patients. Significant differences in clinical characteristics existed between patients selected for NAC versus AC. Two studies demonstrated no survival difference by chemotherapy timing for TN patients, with the third showing improved likelihood of survival after AC for TN patients. No difference was seen for patients with luminal A cancer. Our scoping review reveals a significant gap in the existing literature regarding optimal timing of chemotherapy for modern-era patients receiving targeted therapy based on receptor subtype. Review of the identified studies identified methodological challenges to answering this question through observational study designs.