Immunogenicity of SARS-CoV-2 vaccination in subjects on active treatment for breast cancer

ABSTRACT

Background: Infection with SARS-CoV-2 has led to a global pandemic and has significantly impacted the care of cancer patients. Breast cancer patients receiving active systemic therapy need protection against COVID19 but the efficacy of vaccines in this population is unknown. Although specific biomarkers associated with protection from SARS-CoV-2 infection have yet to be identified, measurement of serum antibody activity is generally accepted as a surrogate of in vivo humoral response to vaccine. This study evaluates the efficiency and durability of binding antibodies to SARS-CoV-2 spike (S) protein in response to COVID19 vaccine in breast cancer patients receiving systemic treatment. Methods: Breast cancer patients, who were unvaccinated, partially or fully vaccinated with Pfizer-BioNTech BNT162b2 (PF), Moderna mRNA-1273 (Mod) or Johnson & Johnson AD26.COV2.S (J&J) were enrolled in this prospective longitudinal study. Eligible patients were on systemic treatment with cytotoxic chemotherapy, chemotherapy plus a checkpoint inhibitor (CPI), CPI alone or a CDK 4/6 inhibitor. Longitudinal blood samples are being collected at baseline, prior to vaccination in unvaccinated patients (T0), 2 weeks after the first vaccine dose and before Sthe second dose for the mRNA vaccines (T1), 1 month (T2), 3 months (T3), 6 months (T4) and 12 month post vaccination. For J&J, there was no T1 timepoint. Roche Elecsys® Anti-SARS-CoV-2 S receptor binding domain (RBD) antibody immunoassay was used to measure antibody titers (range 0.4 to 250 U/mL). Cut points of <0.8 U/mL = negative, ≥0.8 U/mL = seropositive, were based on validated product specifications. Results: Of the 84 breast cancer patients enrolled, 9 had documented COVID infection at baseline and were excluded from analysis. Mean age was 58 years;99% were female, 85% were Caucasian, 49% had early stage disease and 51% had metastatic breast cancer. 67% were receiving cytotoxic chemotherapy, 20% a CKD 4/6 inhibitor, 13% a CPI with or without chemotherapy. 61.2% were vaccinated with PF, 34.3% with Mod and 4.5% with J&J vaccines. Seropositivity rate for the entire group was 10% at T0, 78% at T1, 98% at T2 and 100% at T3. Seropositivity rates of all cohorts at different timepoints are shown in the table. Mean titers for all patients were 12.6 U/mL at T0, 102.3 U/mL at T1, 204.4 U/mL at T2 and 214.6 U/mL at T3 timepoints. Similar incremental increase in antibody levels was observed in all cohorts (Table). Conclusions: 78% of the patients with breast cancer on active systemic treatment were seropositive after the first dose of COVID19 vaccine and 98% after the second dose. The antibody response was maintained at 3 months, with 100% seropositivity rate. 6-month antibody response will be available at the time of presentation. Durability of antibody response at 6 and 12 months will help determine the timing of additional vaccine booster doses in this population. Importantly, this study has found that active treatment with chemotherapy, immunotherapy or CDK4/6 inhibitor therapy does not impact antibody response to SARS-CoV-2 vaccination in patients with breast cancer. Table Seropositivity rate and mean Anti-S protein antibody levels by cohort at each time point. T0= baseline, T1=after first vaccine dose (mRNA vaccines), T2= 4 weeks after 2 doses of mRNA vaccine or after single dose of J&J vaccine, T3=3 months after the first dose of vaccine.