Merck's Keytruda Receives FDA Approval in Combination with Chemotherapy for First-Line Treatment of HER2-Negative Gastric Cancer

On November 16, MSD announced that Keytruda (Pembrolizumab) received FDA approval for a new indication, to be used in combination with chemotherapy as a first-line treatment for locally advanced unresectable or metastatic HER2-negative gastric cancer or gastroesophageal junction (GEJ) adenocarcinoma.

The FDA's approval this time is mainly based on the positive data from the Phase III KEYNOTE-859 study. The study included a total of 1,579 patients and aimed to evaluate the efficacy and safety of Keytruda in combination with PF (5-fluorouracil + cisplatin) or CAPOX (capecitabine + oxaliplatin) compared to placebo combined with PF/CAPOX as a first-line treatment for HER2-negative locally advanced unresectable or metastatic gastric cancer or GEJ adenocarcinoma. The primary endpoint was overall survival (OS), and secondary endpoints included progression-free survival (PFS), objective response rate (ORR), duration of response (DOR), etc.

The study results showed that in the overall population (regardless of PD-L1 expression status), after a median follow-up of 31.0 months (15.3-46.3 months), the median OS of patients in the Keytruda group was significantly longer than that in the chemotherapy group (12.9 vs. 11.5 months), with a 22% reduction in the risk of death (HR=0.78; 95% CI: 0.70-0.87; P<0.0001).

An exploratory analysis of PD-L1 negative patients (CPS <1) found that the median OS was 12.7 months in the Keytruda group and 12.2 months in the chemotherapy group, with an HR of 0.92.

For secondary endpoints, the median PFS (6.9 vs. 5.6 months) and median DOR (8.0 vs. 5.7 months) were significantly prolonged in the Keytruda group, with a 24% reduction in the risk of disease progression or death (HR=0.76; 95% CI: 0.67-0.85; P<0.0001); the ORR was also higher in the Keytruda group compared to the placebo group (51.3% vs. 42.0%, P=0.00009).

In summary, regardless of the patient's PD-L1 expression, the primary endpoint OS and secondary endpoints PFS and ORR were statistically improved. In terms of safety, the proportion of patients experiencing grade 3-5 treatment-related adverse events (TRAEs) was 59.4% in the Keytruda group and 51.1% in the placebo group.

Statistics show that the 5-year survival rate for patients with metastatic gastric cancer is only 6%, of which 80% are HER2-negative gastric cancer. The treatment needs of these patients are yet to be met.

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