A paper just published in Clinical Cancer Research has suggested that — at least for one immunotherapeutic agent (“vaccine”) in development for the treatment of advanced prostate cancer — it may be possible to define a subgroup of men who are more likely to respond well to treatment than others.
Prostvac-VF isa pox-virus-based imunotherapeutic agent that is currently in Phase III clinical trials for the treatment of men with metastatic, castration-resistant prostate cancer. Data from a Phase II clinical trial of this agent, reported back in 2009 at the annual meeting of the American Society of Clinical Oncology, suggested that this agent was capable of inducing a very significant overall survival benefit (of 8.2 months).
Now, Campbell et al. have published data from a study designed to look at whether patients with specific antibodies in their blood (serum), and who participated in that randomized Phase II trial (and other Phase II trials of the same drug), were more likely to benefit from treatment with Prostvac VF than patients who did not carry such serum antibodies.
In their current study, Campbell et al. looked at data and blood samples from 141 patients. Specifically, they used a so-called “glycan microarray” to look for antiglycan antibody populations in the patients’ serum samples before their treatment with Prostvac-VF that might correlate with good response to treatment.
Here is what they found:
- Patients’ antibody levels to blood group A trisaccharide (anti-BG-Atri) before Prostvac-VF treatment had a statistically significant correlation with patient survival.
- Survival of patients with high levels of anti-BG-Atri immunoglobulin M (IgM) had overall survival times that were nearly twice as long as those of patients with little or no anti-BG-Atri IgM pre-treatment.
- This correlation between survival and pre-treatment levels of anti-BG-Atri IgM was specific to treatment with Prostvac-VF.
- There was no such correlation in control patients treated with wild-type poxviruses lacking the key tumor antigen, the PSA molecule.
- There was no such correlation between patients’ anti-BG-Atri IgM levels and “standard” measures of disease severity, such as PSA levels, Gleason scores, or predicted survival (estimated through use of the Halabi nomogram).
This is an extremely interesting finding. Not only does it suggest that we may be able to use glycan microarray technology to evaluate which patients will be good candidates for treatment with Prostvac-VF (if this product does show a survival benefit in the Phase III trials and go on to get approval), it also suggests that we may be able to use this technology in the development of other, newer immunotherapeutic treatments to be used in the management of prostate cancer (and potentially other forms of cancer too).