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Promising response rate in pretreated metastatic gastric cancer with Pembrolizumab

Pembrolizumab (pembro) has shown a promising response rate in patients with pretreated metastatic gastric cancer, according to late-breaking results from the KEYNOTE-059 trial presented today at the ESMO 2017 Congress in Madrid.

Very few new drugs have been approved for this disease in the past decade. The phase II KEYNOTE-059 is one of the largest studies to investigate immunotherapy in recurrent or metastatic gastric cancer.

The study included three cohorts: 1) 259 patients with metastatic gastric cancer who received the programmed death 1 (PD-1) inhibitor pembro alone, after pretreatment with two or more lines of chemotherapy; 2) 25 patients with newly diagnosed metastatic gastric cancer who received a combination of pembro and chemotherapy; 3) 31 patients with newly diagnosed metastatic gastric cancer who received pembro alone. The primary endpoints were safety and objective response rate (OR).

After a median follow-up of six months, the investigators found an OR of 12% with pembro alone in cohort one. Patients who expressed PD-L1 were more likely to respond than those who did not, with objective response rates of 16% and 6%, respectively. Many of the responses were durable. Grade 3 to 5 treatment-related adverse events occurred in 18% of patients in cohort one and 3% had to discontinue treatment as a result.
Lead author Dr Zev Wainberg, co-director of the Gastrointestinal Oncology Programme, UCLA, Los Angeles, US, said: »The data shows that the tumours were sufficiently shrunk to warrant a response. The expected response rate in these heavily pretreated patients was close to zero so the findings are encouraging. These results have set the stage for a larger follow-up study which is already enrolling patients.”

Commenting on the results for ESMO, Dr Ian Chau, consultant medical oncologist, Royal Marsden Hospital, London and Surrey, UK, said: »There is currently no standard of care for metastatic gastric cancer treated in the third line or beyond. The KEYNOTE-059 cohort 1 results confirm that the efficacy previously reported for the PD-1 inhibitor nivolumab in patients from East Asia in the ONO-4538 randomised trial can be applied to Western populations.”
Chau cautioned that while the toxicity profile of pembrolizumab looked quite favourable in KEYNOTE-059, it could be that patients had not been treated long enough to experience side effects. He said: »Unlike with chemotherapy, toxicities from immunotherapy tend to occur later on. We need to await longer-term results from an ongoing clinical trial in an earlier line of treatment to know the full impact of this drug in metastatic gastric cancer.”

#LBA28_PR Wainberg ZA et al: Update: Efficacy and Safety of Pembrolizumab Alone or in Combination with Chemotherapy in Patients With Advanced Gastric or Gastroesophageal (G/GEJ) cancer

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