A multicenter phase II study of vaccines to prevent recurrence in patients with HER-2-positive breast cancer.

532 Background: Patients (pts) with early stage HER2-positive breast cancer are commonly treated with neoadjuvant HER2-targeted therapy. Pts who have residual invasive disease have a less favorable outcome and increased risk of recurrent disease than pts with a complete pathologic response (pCR). It also has been observed that pts who do not achieve a pCR have low or absent anti-HER-2 CD4 Th1 responses. We hypothesized that correcting anti-HER-2 CD4 Th1 response using vaccines will be safe, induce anti-tumor immunity in HER2-positive breast cancer and reduce the risk of recurrence. We conducted a multi-center, phase 2, randomized study to determine the safety, immunogenicity and recurrence free survival of two HER2 vaccines (multivalent anti-oncodriver DNA vaccine (WOKVAC) or HER-2-pulsed dendritic cell vaccine (DC1)). Methods: Pts with HER2-positive early breast cancer were eligible if they had residual invasive disease at surgery after receiving neoadjuvant chemotherapy plus HER2-targeted therapy. Patients were randomly assigned in a 1:1 ratio, with stratification according to residual cancer burden (RCB) (1+2 vs 3) to receive adjuvant HER2 vaccination with either DC1 or WOKVAC. For the initial vaccination phase, DC1 was delivered via US guided inguinal lymph node administration, weekly x 6 weeks and WOKVAC was given intradermally on weeks 1, 4, and 7. Booster vaccines were given at months 6, 9 and 12. The primary end point is to evaluate the safety and tolerability of each vaccine and assess immune response rate as measured by ELISPOT. Each treatment arm will be assessed separately. Secondary endpoints include recurrence-free survival. Exploratory analyses include the assessment of prognostic and predictive biomarkers including circulating tumor cells, serum HER2 levels, and other immune correlative biomarkers. Here we are reporting the initial safety results. Results: Total of 110 eligible pts (55 WOKVAC vs 55 DC1) were enrolled from 2/2018 to 12/2022 and received at least one dose of treatment and 38 pts pending completion of the booster phase. Most pts had clinical stage II/III 56/35 (82%) and 50% had positive node disease at diagnosis. 82% had hormone receptor positive disease. 37/38/8 patients had RCB 1/2/3. For patients without known RCB status, ypTNM was used to randomize (yp stage I/II/III = 13/13/1 pts). The most frequently observed treatment related adverse events (TRAE) were injection site pain/reaction (38%) and chills (34%), fever (25%) and fatigue (40%) for DC1 arm. For WOKVAC, the most common toxicities included injection site reaction (68%) and fatigue (37%). All of these were grade 1 and 2. Nine patients had events including new primary cancer (1), local recurrence (2), metastatic disease recurrence (6). Conclusions: Both DC1 and WOKVAC HER2 vaccines were well tolerated without significant toxicities. Updated results will be presented at the meeting including correlatives. Clinical trial information: NCT03384914 .