Neoadjuvant immunotherapy in breast cancer: a paradigm shift?

Despite advances in clinical management, a proportion of patients with early-stage triple-negative breast cancer (TNBC) recur after local treatment. The concept of neoadjuvant systemic therapy has been widely adopted to improve clinical outcomes of patients with TNBC and other breast tumour types. Recently, promising data were reported from the first prospective phase III, randomised trial assessing neoadjuvant chemotherapy combined with the programmed cell death protein 1 (PD-1) inhibitor pembrolizumab versus placebo in patients with early-stage TNBC. The addition of pembrolizumab resulted in a significant increase in pathologic complete response (pCR) rates. Similarly, in the IMpassion031 trial, the use of atezolizumab in combination with neoadjuvant chemotherapy in patients with early-stage TNBC led to improved pCR rates compared to placebo, regardless of programmed death ligand 1 (PD-L1) expression. Ongoing trials are testing other PD-1/PD-L1 inhibitors in combination with neoadjuvant chemotherapy in TNBC and other tumour subtypes. However, not all patients benefit from the addition of immunotherapy, while a proportion of patients experiences serious adverse events. It is critical to identify predictive biomarkers of response, to accurately select patients who will benefit from immunotherapy, thus sparing the rest from ineffective treatments with unnecessary toxicity and treatment costs. In this review, we summarise the literature on reported and ongoing neoadjuvant clinical trials evaluating immunotherapy in breast cancer.