With under 40 patients enrolled in the whole study and just 17 in the DCV-treated arm, it was always likely to be ambitious to make significant conclusions about biomarkers for response or lack of response to the therapies. But what can be derived from this study?
“I do think [the researchers] will likely see predictive value in these results when they analyze a big enough data set. Adding in another level of complexity (sPD-L1) to this particular paper with the low numbers of patients was probably unrealistic,” said Dr Bartee.
Although this study was undoubtedly an early, preliminary look into sPD-1 as a biomarker, it may set an important precedent for future work, not least because sPD-1 from blood would represent an easy, minimally invasive way to track levels of the protein throughout disease progression or response to therapies.
“This is a marker that you can get without having to do a tumor biopsy, and in addition, you can easily get it over different time points. For tumor biopsy, doing this at multiple time points can be very difficult and technically tricky. In one area of the tumor you might also get a different pathology than in another. It’s a huge potential advantage to look at sPD-1,” said Dr Buchbinder.
Notably, the research was also conducted before immune checkpoint inhibitors of PD-1/PD-L1 were frequently used, but nevertheless, the results are likely relevant to the future of sPD-1 as a possible biomarker.
“I think the researchers are on a good track here, but there have just been so many things suggested as prognostic indicators. None is perfect, but all of them do have some value. In the grand scheme of things, sPD-1 is likely another one that will have some value, but [will] not be perfect by itself,” said Dr Bartee, stressing that a much larger study was needed with big data sets involving hundreds of patients from multiple trials, to validate the results.
“sPD-1 is a very interesting potential biomarker, as it may be able to provide insight into predicting which patients you could even give less therapy than more, particularly in melanoma. Obviously, [as] it was only a small number of patients, they would need plenty more before it could potentially be used for clinical decision making,” said Dr Buchbinder.
- Dillman RO, Nistor GI, McLelland BT, et al. Preliminary observations on soluble programmed cell death protein-1 as a prognostic and predictive biomarker in patients with metastatic melanoma treated with patient-specific autologous vaccines. Oncotarget. 2019;10(51):5359-5371.
- Dillman RO, Cornforth AN, Depriest C, et al. Tumor stem cell antigens as consolidative active specific immunotherapy. J Immunother. 2012;35(8):641-649.