Background: I-SPY 2 is a multicenter, phase 2 trial using response-adaptive randomization within molecular subtypes defined by receptor status and MammaPrint (MP) risk to evaluate novel agents as neoadjuvant therapy for women with high-risk stage II/III breast cancer. The primary endpoint is pathologic complete response (pCR, ypT0/Tis ypN0). SGN-LIV1A is an investigational antibody drug conjugate consisting of an antibody to LIV1A, a zinc transporter highly prevalent in breast cancer, and a highly potent microtubule inhibitor, monomethyl auristatin E. Retrospective IHC analysis of LIV1A expression levels amongst tumor samples from 100 previous ISPY-2 patients showed 88% of breast tumor samples with moderate to high expression of LIV1A (Yau, C. et al SABCS 2018).Methods: Women with tumors ≥ 2.5cm were eligible for screening. Only HER2 negative (HER2-) patients were eligible for this treatment, hormone-receptor positive (HR+) patients had to have MP high molecular profile. Treatment included SGN-LIV1A 2.5 mg/kg (max dose 250 mg) every 3 weeks x 4, followed by doxorubicin/cyclophosphamide (AC) every 2-3 weeks x 4. The control arm was weekly paclitaxel x 12 followed by AC every 2-3 weeks x 4. All patients undergo serial MR imaging where response at 3 & 12 weeks combined with accumulating pCR data are used to estimate, and continuously update, predicted pCR rate for the trial arm. Analysis set was modified intention to treat with patients who switched to non-protocol therapy counted as non-pCR and not as their pCR status at time of surgery. The goal is to identify/graduate regimens with ≥85% Bayesian predictive probability of success (i.e. demonstrating superiority to control) in a future 300-patient phase 3 neoadjuvant trial with a pCR endpoint within signatures defined by HR & HER2 status & MP result. This investigational arm was eligible for graduation in 3 of 10 pre-defined signatures: HER2-, HR+HER2- and HR-HER2-. Regimens may also leave the trial for futility (< 10% probability of success), maximum sample size accrual (10% < probability of success <85%), maximum time in trial (2 years) or for safety as recommended by the independent DSMB.

Results: Sixty patients were randomized and evaluable to SGN-LIV1A. The study arm was stopped due to reaching the predetermined time limit for patient accrual of 2 yrs. Final estimated pCR rates are below. The estimated pCR rates were similar between the SGN-LIV1A and control arms for any tumor subtype. Preliminary safety events for SGN-LIV1A include increased rates of transaminitis and hyperglycemia and reduced rates of peripheral neuropathy compared to control. One patient was removed from the analysis as she was determined to have angiosarcoma of the breast. Notably, this patient had a dramatic early response and subsequent pCR to SGN-LIV1A treatment. Conclusion: The value of I-SPY 2 is to give insight about the performance of an investigational agent’s likelihood of achieving pCR. SGN-LIV1A delivered every 3 weeks was comparable to paclitaxel for the primary endpoint of pCR in I-SPY2 and may have a similar side effect profile, however, with less peripheral neuropathy. Clinical trials evaluating weekly dosing of SGN-LIV1A are ongoing. A trial of SGN-LIV1A in the treatment of angiosarcoma is under consideration at this time.

Final Estimated pCR Rates and Predictive Probabilities
Estimated pCR rate(95% prob interval)
Signature SGN-LIV1A Control Probability SGNLIV1A Superior to Control Predictive Probability of Success in Phase 3 
HER2- 0.16 (0.08-0.24) N= 60 0.20 (0.16-0.25) N= 327 0.18 0.02 
HR-/HER2- 0.25 (0.12-0.37) N=36 0.28 (0.21-0.35) N=146 0.31 0.06 
HR+/HER2- 0.09 (0-0.18) N=24 0.14 (0.09-0.19) N=181 0.15 0.03 
Final Estimated pCR Rates and Predictive Probabilities
Estimated pCR rate(95% prob interval)
Signature SGN-LIV1A Control Probability SGNLIV1A Superior to Control Predictive Probability of Success in Phase 3 
HER2- 0.16 (0.08-0.24) N= 60 0.20 (0.16-0.25) N= 327 0.18 0.02 
HR-/HER2- 0.25 (0.12-0.37) N=36 0.28 (0.21-0.35) N=146 0.31 0.06 
HR+/HER2- 0.09 (0-0.18) N=24 0.14 (0.09-0.19) N=181 0.15 0.03 

Citation Format: Heather Beckwith, Richard Schwab, Christina Yau, Erica Stringer-Reasor, Shi Wei, A. Jo Chien, Kathy S Albain, Kevin Kalinsky, Anne Wallace, Anthony Elias, Douglas Yee, Amy S Clark, Judy C Boughey, Heather Han, Rita Nanda, Claudine Isaacs, Zahi Mitri, Julie E Lang, Alexandra Thomas, Tara Sanft, Angela DeMichele, Jane Perlmutter, Hope S Rugo, Nola M Hylton, W. Fraser Symmans, Michelle E Melisko, Laura J van't Veer, I-SPY 2 Consortium, Amy Wilson, Smita M Asare, Ashish Sanil, Donald A Berry, Laura J Esserman. Evaluation of SGN-LIV1a followed by AC in high-risk HER2 negative stage II/III breast cancer: Results from the I-SPY 2 TRIAL [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 PD1-10.