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

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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 ISPY-2 clinical trial. Methods Patients had stage 2–3 HER2-negative breast cancer in a single institution. Regimens included: weekly paclitaxel (control), weekly paclitaxel in combination with pembrolizumab, or weekly paclitaxel in combination with pembrolizumab and intra-tumoral injection of SD-101, a TLR9 agonist. All patients then received AC and underwent surgery. Regional lymph nodes were retrospectively evaluated on breast MRI at baseline, 3 wks, 12 wks and 20 wks by a single blinded radiologist. MRIs were assessed for development of new regional lymphadenopathy, or increase in longest diameter or cortical thickness of largest regional lymph node. Results Between 12/2015-4/2021, a total of 43 patients enrolled to the control (n = 16) and paclitaxel + pembrolizumab +/- SD-101 (n = 27) arms. 25 patients had hormone-receptor positive disease and 18 patients had triple negative disease. 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). 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 (p = 0.696) or immune-related toxicity. Conclusions Chemo-immunotherapy was associated with early increases in regional lymphadenopathy despite decreased breast tumor size. Increased lymphadenopathy was not associated with node-positive disease at surgery.