The most important application of biomarkers in cancer immunotherapy is the potential to identify and select patients who are most likely to respond. Unfortunately, we know that not all patients respond to immunotherapy. If we take the example of ipilimumab, 20% of patients achieve a long-term benefit, another 60% have a benefit which can be of a few (3–4) months or longer (1–2 years), while for the other 20% – treatment has no beneficial effect . Clearly, it would be helpful to know which one of these three different groups a patient belongs to before deciding on whether to treat with ipilimumab.
With anti-PD-1 agents, we still do not have data in terms of long-term benefit. However, the response rate is approximately 40%, and around 60% of patients are still alive after 2 years . Thus, it is apparent that not all patients benefit from anti-PD-1 therapy. Moreover, it is recommended that these agents are used until disease progression, meaning that patients could be treated for years. Considering the high cost of these treatments, having a biomarker that could predict outcome would be very useful in helping to target therapy at those likely to respond. Unfortunately, we do not yet have this kind of biomarker.
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