The introduction of immunotherapies in oncology has caused a paradigm shift in cancer treatment. By exploiting the adaptive immune system’s ability to reject cancers, these therapies have allowed a substantial revolution.
Anti-PD-1/PD-L1 antibodies demonstrated durable efficacy in patients with melanoma, renal cell carcinoma (RCC), and non-small-cell lung cancer (NSCLC), which are cancer types where response is predicted to be highest, combining long-term outcomes with an optimal safety profile.
Unfortunately, the high cost of immunotherapeutic drugs and the associated low response rates (under 20% in selected cancer types) have raised some concern about the economic sustainability of these treatments, with payers calling for the identification of positive-predictive biomarkers of immunotherapy response.
PD-L1 expression is now inconsistently being used to predict the response to checkpoint blockade. However, due to high variability in the response of PD-L1–positive tumours, there is still no consensus regarding its value as a positive-predictive biomarker.
A Phase II study found that patients with colorectal cancer (CRC) who have deficient mismatch repair mechanism, resulting in high microsatellite instability (MSI-H) and high differentiation, had a potent and durable response to immune checkpoint blockade with Merck & Co.’s Keytruda (pembrolizumab). The trial demonstrated an almost tripled response rate (from 20% to approximately 57%) and the achievement of disease control in 89% of the patients for up to 36 weeks. Unfortunately, MSI-H CRC accounts for only 4% of the metastatic CRC population.
In the past, biomarker restrictions on the treatment-eligible population had served as hurdles to the drug development process, slowing down clinical trial recruitment and decreasing economic incentives. Despite the identification of a positive-predictive biomarker might be rewarded by a higher reimbursement price, the limitation of the patient pool can limit the commercial reward.
Keytruda is an example of how highly efficacious immunotherapies are changing the status quo of biomarker-driven drug development in oncology. Although Keytruda will be approved in 2017 for MSI-H metastatic CRC only, with a very limited eligible patient population, the drug’s uptake in this subset of patients is expected to be substantial because of its unprecedented efficacy. Further, according to trial results, CRC patients could be treated with Keytruda for up to two years.
According to GlobalData’s recently published report on CRC, the extended duration of treatment is expected to guarantee Merck & Co. consistent sales, making Keytruda a blockbuster in CRC less than ten years after its approval ($1.29bn by 2025). This satisfies the needs of developers, payers, and CRC patients, who will be offered for the first time a potential chance of cure.