Abstract PS3-09: The use of magnetic resonance imaging (MRI) in predicting pathological complete response(pCR) in the breast and axilla after the addition of immunotherapy to neoadjuvant systemic therapy (NST)
Authors: Rajarajan Noeline , Segarra Daniel , Weinfurtner Robert J , Lopez Adrian A , Lee M Catherine , Kiluk John , Soliman Hatem , Khong Hung , Hyo Han S , Rosa Marilin , Czerniecki Brian J , Khakpour Nazanin 
Published: February 2021

Introduction: Immunotherapy use is increasing as an adjunct to current NST for breast cancer treatment with the goals of increasing pCR and down staging tumors. In this study, we assessed the effectiveness of MRI in the evaluation of tumor response after neoadjuvant immunotherapy in combination with NST. Methods: We retrospectively reviewed the clinicopathological data of 105 women undergoing Immunotherapy in conjunction with NST at a single institution. All patients had been enrolled in IRB approved protocols and had undergone definitive surgery. Patients were excluded for: failure to complete at least two thirds of treatment, no pre or post treatment MRI, or surgery in an outside institution. We analyzed 73 patients from 5 distinct treatment protocols including: (1) 24 Triple negative breast cancer (TNBC) patients (pts) treated with Intratumoral Talimogene laherparepvec (TVEC) in combination with weekly paclitaxel followed by dose dense Adriamycin and Cytoxan (ddAC); (2) 19 HER2/Neu positive (HER2+) pts treated with subcutaneous interferon gamma (IFN-γ) in combination with weekly paclitaxel with trastuzumab and pertuzumab (HP); (3), 7 HER2+ pts treated with 3 weeks of HER2 pulsed dendritic cell vaccines (DC1) followed by Taxotere, Carboplatin, and HP; (4), 14 pts on the ISPY2 trial: 8 TNBC and 4 Hormone receptor positive, HER2/Neu negative (HR+) pts randomized to treatment with pembrolizumab with weekly paclitaxel followed by ddAC (2 also received additional SD101), and 2 TNBC pts treated with Durvalumab, Olaparib and Paclitaxel, followed by ddAC and (5) 9 HR+ pts on neoadjuvant Durvalumab and an Aromatase Inhibitor for 6 cycles. Results: A total of 73 patients were included in the study. Median age was 51 years (range 27-76); 46.6% of patients had TNBC, 35.6% had HER2+ and the remaining 17.8% were HR+ HER2-. The median clinical tumor size was 3.4cm (range 1.3-10.6) pre therapy and 1cm (range 0-10.1) post therapy. The pCR was 38.2%, 57.7%, and 0% respectively for TNBC, HER2+, HR+ tumors. Complete radiological response (rCR) of both the axilla and breast was 41.2%, 61.5% and 7.7%, for TNBC, HER2+ and HR+ tumors. The sensitivity of MRI to detect in breast pCR was 65.6% with a specificity of 81%, NPV and PPV of 75% and 73.3% respectively. MRI identified 37 pts with suspicious axillary nodes on pretreatment MRI; of these 30 had fine needle aspiration (FNA) confirmed metastatic disease. Post treatment, 70.3% (26/37) had normalized axillary nodes. Of those with normalized nodes, 26.9% (7/26) had residual cancer on final pathology. Of the patients with confirmed FNA lymph node metastasis, axillary pCR of 63.3% was achieved. The sensitivity and specificity of MRI to detect pCR within the axilla was 87% and 50% and NPV and PPV 70% and 74.1%, respectively. 3 patients had axillary disease on final pathology but no suspicious imaging and a benign FNA. Conclusion: The addition of immunotherapy to current NST strategies can improve pCR and decrease residual cancer burden. The PPV and NPV of MRI to predict pCR in patients undergoing immunotherapy in combination with NST remains within the ranges described in patients undergoing NST alone. MRI remains a useful tool to guide surgical management but is not accurate enough to replace pathological evaluation.

Citation Format: Noeline Rajarajan, Daniel Segarra, Robert J Weinfurtner, Adrian A Lopez, M Catherine Lee, John Kiluk, Hatem Soliman, Hung Khong, Han S Hyo, Marilin Rosa, Brian J Czerniecki, Nazanin Khakpour. The use of magnetic resonance imaging (MRI) in predicting pathological complete response(pCR) in the breast and axilla after the addition of immunotherapy to neoadjuvant systemic therapy (NST) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS3-09.