Cancer vaccines: can they improve survival?

In patients with metastatic cancer, therapeutic anticancer vaccines are rarely associated with objective antitumor responses; so, many investigators have focused on progression-free survival (PFS) as a key endpoint for clinical trials. However, it is not clear that PFS is a surrogate for overall survival (OS), and OS may be a more appropriate endpoint because of the effects on long-term memory in the adaptive immune system. Recently, reported vaccine trials were reviewed to determine their primary and secondary endpoints and results. Randomized trials testing sipuleucel-T and prostvac-vf in prostate cancer and ipilimumab and eltrapuldencel-T in melanoma were associated with low objective response rates, no improvement in PFS, but statistically significant improvement in OS. Although compared with PFS, it takes longer to get a final result when OS is the primary endpoint; there is increasing evidence that if long-term memory recognition of tumor-associated antigens is the mechanism of action of an investigational product, then OS may be the only valid clinical endpoint for efficacy.