Regional lymph node changes on breast MRI in patients with early-stage breast cancer receiving neoadjuvant chemo-immunotherapy

Abstract Purpose Establishing breast MRI imaging patterns associated with neoadjuvant immunotherapy is needed to monitor response. We analyzed serial breast MRIs in patients receiving neoadjuvant chemo-immunotherapy on the I-SPY2 clinical trial. Methods Patients with stage 2–3 HER2-negative breast cancer were randomized to weekly paclitaxel (control), weekly paclitaxel and pembrolizumab, or weekly paclitaxel, pembrolizumab and intra-tumoral injection of SD-101, a TLR9 agonist. All patients received AC. Regional lymph nodes were retrospectively evaluated on breast MRI at baseline, 3, 12 and 20 weeks by a single blinded radiologist. MRIs were assessed for development of new regional lymphadenopathy, or increase in the longest diameter or cortical thickness of the largest abnormal regional lymph node. Results Between 12/2015 and 4/2021, a total of 43 patients enrolled in the control ( n = 16) and paclitaxel + pembrolizumab ± SD-101 ( n = 27) arms. 12 of 27 patients (44.4%) receiving chemo-immunotherapy experienced increased lymphadenopathy within the first 12 weeks compared to 1 of 16 patients (6.3%) in the control group ( p = 0.014). Most patients with increased lymphadenopathy were in the SD101/pembro arm ( n = 10, p = 0.002). Increased lymphadenopathy was observed despite concomitant decrease in breast tumor size at all time points. 11 of 12 patients with increased lymphadenopathy had pathologically negative nodes at surgery. There was no association between lymphadenopathy and lower residual cancer burden or immune-related toxicity. Conclusions The combination of neoadjuvant paclitaxel and pembrolizumab ± SD101 intratumoral injection was associated with early increases in regional lymphadenopathy on MRI despite decreased breast tumor size. Increased lymphadenopathy was not associated with node positive disease at surgery.