Thirty-Five-Year Follow-Up Real-World Data Revealed the Efficacy of Autologous Formalin-Fixed Tumor Vaccine on Metastatic Breast Cancer-A Target Trial Emulation.

Background and methods: The prognosis after distant metastasis of breast cancer is generally poor. We analyzed the effect of an autologous formalin-fixed tumor vaccine (AFTV) on postoperative breast cancer using 35-year follow-up real-world data in a concurrent cohort and a target trial emulation, a similar method to the randomized study. The sample (n = 698) was narrowed to cases with distant metastasis, resulting in a cohort of 94 patients. In this study, meta-OS refers to overall survival after distant metastasis.

Results: Treatment with AFTV significantly prolonged meta-OS. The median meta-OS was 4.58 years for the AFTV group (n = 59) compared to 2.81 years for the control group (n = 35), with a significant difference (P = .0300). Radiotherapy (RT), a stratified factor, also extended meta-OS, although no superiority was observed between AFTV therapy and RT in multivariable regression analysis. The combination of AFTV therapy and RT demonstrated a synergistic effect in prolonging meta-OS (P = .0320). Chemotherapy (Chemo) alone showed no significant effect on meta-OS in the control group but shortened meta-OS in the AFTV group, if administered within 6 months of AFTV treatment (P = .0478). Treating after distant metastasis, the "Optimum AFTV Set" subgroup (AFTV therapy plus RT without Chemo within 6 months, n = 13) extracted from the AFTV group had a median meta-OS of 12.85 years, showing a significant improvement compared to the corresponding control subgroup (RT without Chemo within 6 months) (n = 6, P = .00819). The 10-year survival rate after distant metastasis was 25.6% in the AFTV group, 7.4% in the control group, 53.8% in the Optimum AFTV Set subgroup, and 0% in the corresponding control subgroup. All AFTV-related adverse events were classified as CTCAE grade 2 or lower.

Discussion: The results of Optimum AFTV Set therapy provide a strong rationale for a larger-scale prospective randomized study.

Conclusion: The present real-world data suggest that Optimum AFTV Set therapy may be a useful option for treatment following the detection of distant metastasis after breast cancer surgery.