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Encouraging data for PD-1 inhibitor pembrolizumab in different PD-L1-positive tumors
Pembrolizumab (MK-3475; Merck & Co.) is a highly selective anti-PD-1 humanized monoclonal antibody (MAb) that has shown antitumor activity in several types of cancer, is not cytotoxic and can be administered every 2 or 3 weeks, as seen in previous pharmacokinetic studies.
Researchers in Japan reported initial data corresponding to patients with gastric cancer being treated in one of the cohorts of the KEYNOTE-012 study (ClinicalTrials.gov Identifier NCT01848834), a phase Ib trial intended to evaluate the safety, tolerability and efficacy of pembrolizumab in patients with different types of advanced solid tumors. Patients (n = 19 Asian; n = 20 non-Asian) were treated with i.v. pembrolizumab 10 mg/kg every 2 weeks and were followed up to 24 months until complete response, disease progression or unacceptable toxicity. The more frequent treatment-related adverse events (TEAEs) were hypothyroidism and fatigue, both in 12.8% of patients, with no patient discontinuations. The primary efficacy endpoint of overall response rate (ORR) showed strong evidence of antitumor activity in both groups, 30 and 31.6% for non-Asian and Asian subjects, respectively, and a phase II in this type of cancer is planned to begin enrollment shortly (Muro, K. et al. 39th Eur Soc Med Oncol (ESMO) Congr (Sept 26-30, Madrid) 2014, Abst LBA15).
Other results from the multi-cohort KEYNOTE-012 trial were presented regarding the cohort of patients with recurrent or metastatic HPV+ and HPV- head and neck squamous cell carcinoma (HNSCC). Patients (N = 60; median age = 63 years) received i.v. pembrolizumab 10 mg/kg every 2 weeks until disease progression, unacceptable toxicity or completion of 24 months of treatment. After 10.2 months of follow-up all patients remained on the treatment. Frequent reasons for discontinuation were progressive disease and adverse events (AEs), in 57 and 10% of patients, respectively, and the primary endpoint was ORR and secondary endpoints were progression-free survival (PFS), overall survival (OS) and duration of response. Assessment of antitumor activity revealed that 51% either decreased or maintained the size of their lesions compared with baseline. ORR was 19.6% and was similar in HPV+ and HPV- subjects, and PD-L1 correlated with response. OS was longer in HPV+ than in HPV- tumor patients (73.9 vs. 58.1%) and PFS was also longer, with a median number of weeks of 17.2 for HPV+ and 8.1 weeks for HPV- subjects. The more frequent AEs were fatigue (18.3%) and pruritus (10%). Pembrolizumab was well tolerated and showed antitumor activity in patients with HPV+ and HPV- advanced HNSCC. Phase III studies in this subset of patients will follow the expansion cohort of KEYNOTE-012, currently ongoing (Chow, L. et al. 39th Eur Soc Med Oncol (ESMO) Congr (Sept 26-30, Madrid) 2014, Abst LBA31).
Pembrolizumab has previously shown antitumor activity and tolerability in both treatment-naive and pretreated advanced non-small cell lung cancer (NSCLC) patients. Results of a pooled analysis of patients were allocated in two randomized and three non-randomized cohorts of the phase I KEYNOTE-001 study (ClinicalTrials.gov Identifier NCT01295827). Patients (N = 307) received 2 mg/kg of i.v. pembrolizumab every 3 weeks or 10 mg/kg every 2 or 3 weeks until disease progression or unacceptable toxicity. The most frequently reported AE was fatigue (25%), and in terms of grade 3-5 AEs, the most common was pneumonitis (2%). ORR was 33, 21 and 21% for the dose groups of 2 mg/kg every 2 weeks, 10 mg/kg every 3 weeks and 10 mg/kg every 2 weeks, respectively. Median PFS was 13 weeks, and at 6 months the PFS was 30%, and median OS was 8.2 months and at 6 months it was 64% of the pooled population. Pembrolizumab was safe and showed strong antitumor activity both in treatment-naive and previously treated NSCLC in all treatment subgroups (Garon, E. et al. 39th Eur Soc Med Oncol (ESMO) Congr (Sept 26-30, Madrid) 2014, Abst LBA43).
Early data were also reported in patients allocated in the advanced urothelial bladder cancer cohort of the ongoing phase Ib KEYNOTE-012 study. Patients received pembrolizumab (10 mg/kg every 2 weeks) with a median follow-up of 11 months. Of these, approximately 75% had also received one or more previous treatments. Among patients eligible for response (N = 29), 3 experienced a complete response, 4 a partial response, 4 disease stabilization and 14 disease progression. The most frequent AEs were fatigue (18%), peripheral edema (12%) and nausea (9%). Four patients experienced grade 3 to 4 AEs, with one discontinuation due to TEAEs, and the ORR was 24.1%. A decrease in target lesions was seen in 64% of patients, median time to response was 8 weeks, and median OS and PFS was 9.3 months and 8.6 weeks, with OS and PFS at 6 months of 58.0 and 23.1%, respectively. Pembrolizumab presented an acceptable safety profile and significant antitumor activity when administered as monotherapy in patients with advanced PD-L1-positive bladder cancer. These results led to the initiation of a phase III trial for pembrolizumab in advanced urothelial cancer at the end of 2014 to confirm this anti-PD-1 therapy feasibility for this devastating disease (Plimack, E. et al. 39th Eur Soc Med Oncol (ESMO) Congr (Sept 26-30, Madrid) 2014, Abst LBA23).
To further compare the efficacy and safety of pembrolizumab, an additional 244 patients were enrolled in KEYNOTE-001 and randomized 1:1 to receive pembrolizumab 10 mg/kg every 3 weeks (n = 121) or 10 mg/kg every 2 weeks (n = 123). The median follow-up as of February 2014 was approximately 35 weeks, with all patients having had >= 26 weeks of follow-up. The median treatment duration was 21 weeks for the every-3-weeks arm and 22 weeks for the every-2-weeks arm. No significant difference in ORR was observed between the two schedules, with an ORR of 28% every 3 weeks and 33% every 2 weeks. This consisted of 1 complete response and 29 partial responses in the every-3-week cohort, while 4 complete responses and 34 partial responses were seen in the every-2-week cohort. The 24-week PFS rates were 43% every 3 weeks and 47% every 2 weeks, with no significant difference observed in PFS between schedules. Twelve and 15% of patients receiving the every 3 week and the every 2 week schedule, respectively, reported grade 3 to 4 AEs. Discontinuations due to TEAEs resulted in 1% of patients every 3 weeks and 3% of patients every 2 weeks. No treatment-related deaths were reported. Overall, the results of this study demonstrated that pembrolizumab has similar efficacy and safety at 10 mg/kg every 3 weeks and 10 mg/kg every 2 weeks in patients with advanced melanoma. Since previous randomized data showed no significant difference in efficacy and safety between pembrolizumab doses of 10 mg/kg every 3 weeks and 10 mg/kg every 2 weeks, the recommended pembrolizumab dose and schedule was determined to be 2 mg/kg every 3 weeks (Robert, C. et al. 39th Eur Soc Med Oncol (ESMO) Congr (Sept 26-30, Madrid) 2014, Abst LBA34).
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