Safety run-in phase of the multi-epitope HER2 peptide vaccine in combination with trastuzumab emtansine in HER2-positive breast cancer with residual disease after neoadjuvant chemotherapy.

Saranya Chumsri Mayo Clinic Florida, Jacksonville, FL info_outline Saranya Chumsri, Sharmila Giri, Andrew Ness, David W. Hillman, Nadine Norton, Davitte Cogen, Edward Famularo, Brianna Richardson, Brian Necela, Aziza Nassar, Donald W. Northfelt, Pooja Prem Advani, Rohit Rao, Kostandinos Sideras, Alvaro Moreno-Aspitia, Brenda Ernst, Kathryn Jean Ruddy, Matthew P. Goetz, Keith L. Knutson

Authors Saranya Chumsri Mayo Clinic Florida, Jacksonville, FL info_outline Saranya Chumsri, Sharmila Giri, Andrew Ness, David W. Hillman, Nadine Norton, Davitte Cogen, Edward Famularo, Brianna Richardson, Brian Necela, Aziza Nassar, Donald W. Northfelt, Pooja Prem Advani, Rohit Rao, Kostandinos Sideras, Alvaro Moreno-Aspitia, Brenda Ernst, Kathryn Jean Ruddy, Matthew P. Goetz, Keith L. Knutson Organizations Mayo Clinic Florida, Jacksonville, FL, Mayo Clinic, Rochester, MN, Mayo Clinic Alliance Statistics and Data Center, Rochester, MN, Mayo Clinic Department of Pediatric and Adolescent Medicine, Phoenix, AZ, Mayo Clinic, Phoenix, AZ Abstract Disclosures Research Funding No funding sources reported Background: Residual disease after neoadjuvant chemotherapy (NAC) in HER2-positive breast cancer (BC) confers poor outcomes. Despite additional trastuzumab emtansine (T-DM1) in the adjuvant setting, a significant number of patients with residual disease still develop recurrence. H2NVAC is a multi-epitope T helper cell-activating peptide vaccine that is composed of 4 degenerate HER2-derived HLA-DR epitopes admixed with GM-CSF. Our previous phase I trial showed that this vaccine was safe and generated robust, long-lasting T and B cell immune responses. Methods: Patients with stage II-III HER2+ BC with any amount of residual disease in the breast /axilla after NAC were enrolled in a safety run-in phase of H2NVAC in combination with T-DM1. Patients were treated with H2NVAC and T-DM1 for 6 cycles, followed by 2 boosters at 3 and 12 months. Dose-limiting toxicity (DLT) was defined as any grade (G) ≥ 3 adverse events (AE) occurring within 21 days after the first vaccination. Results: A total of20 patients were enrolled with a median age of 51 years (range 27-69), 80% were White and 15% were Black. Most patients had hormone receptor-positive disease (90%). 40% were premenopausal, 40% were postmenopausal, and 20% were unknown. 14 patients had ypT1, 3 patients ypT2, 3 patients ypT3, 1 patient ypT4, 8 patients ypN0, 9 patients yp N1, 1 patient ypN1mi, and 2 patients ypN2. H2NVAC, in combination with T-DM1, was well tolerated, with no DLT being observed. Only grades 1 and 2 AEs were observed during the DLT period, with fatigue being the most common (G1 60%, G2 5%), followed by peripheral sensory neuropathy (G1 55%, G2 5%) and injection site reaction (G1 50%). Across all treatment cycles, the top 10 most common AEs that were at least possibly related to treatment include injection site reaction (G1 85%, G2 15%), AST increase (G1 65%), ALT increase (G1 45%), fatigue (G1 35%, G2 10%), peripheral sensory neuropathy (G1 35%, G-tube 10%), alk-phos increase (40% G1), nausea (G1 35%, G2 5%), arthralgia (G1 35%), myalgia (G1 25%, G2 5%), and platelet count decrease (G1 30%). There were four patients with G3 AEs at least possibly related to the vaccine observed after the DLT period, including allergic reaction, myositis/skin infection, urticaria, and pruritus/maculopapular rash. Conclusions: H2NVAC, in combination with T-DM1, was safe without DLT observed. The side effect profile was favorable, with the most common AE being the G1 injection site reaction. A multicenter, randomized, placebo-controlled, phase II trial of H2NVAC vs. placebo in combination with trastuzumab emtansine is currently ongoing through the ACCRU consortium. Clinical trial information: NCT04197687.

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