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The FDA ( U.S. Food and Drug Administration ) has approved Keytruda ( Pembrolizumab ), an anti-PD-1 therapy, as monotherapy for the treatment of patients with metastatic small cell lung cancer ( SCLC ) with disease progression on or after Platinum-based chemotherapy and at least one other prior line of therapy.

This accelerated approval is based on tumor response rate and durability of response.
Continued approval for this indication may be contingent upon verification and description of clinical benefit in the confirmatory trials.

The approval was based on pooled data from KEYNOTE-158 ( cohort G ) and KEYNOTE-028 ( cohort C1 ), two multicenter, multi-cohort, non-randomized, open-label trials evaluating Pembrolizumab in patients with SCLC who had disease progression on or after Platinum-based chemotherapy and at least one other prior line of therapy.
The trials excluded patients with autoimmune disease or a medical condition that required immunosuppression.
Among the 83 patients enrolled in the trials and who were evaluated for efficacy, 64% received two prior lines of therapy and 36% received three or more lines of therapy; 60% received prior thoracic radiation therapy; 51% received prior radiation therapy to the brain.

Patients have evaluated for efficacy received either Pembrolizumab 200 mg intravenously every three weeks ( n=64 ) or 10 mg/kg intravenously every two weeks ( n=19 ).
Treatment with Pembrolizumab continued until documented disease progression, unacceptable toxicity or a maximum of 24 months.
Patients with initial radiographic disease progression could receive additional doses of Pembrolizumab during confirmation of progression unless disease progression was symptomatic, was rapidly progressive, required urgent intervention or occurred with a decline in performance status.
The major efficacy outcome measures were objective response rate ( ORR ) and duration of response ( DOR ) as assessed by BICR according to Response Evaluation Criteria in Solid Tumors ( RECIST ) v1.1, modified to follow a maximum of 10 target lesions and a maximum of five target lesions per organ.

Pembrolizumab has demonstrated an ORR of 19% ( 95% CI, 11-29 ), with a complete response rate of 2% and a partial response rate of 17%.
Among the 16 responding patients, 94% had a DOR of six months or longer, 63% had a DOR of 12 months or longer and 56% had a DOR of 18 months or longer.
Responses ranged from 4.1 to 35.8+ months.

Among the patients with SCLC enrolled in KEYNOTE-158 ( cohort G ) ( n=107 ) and KEYNOTE-028 ( cohort C1 ) ( n=24 ) who were included in the safety analysis, the adverse reactions that occurred were similar to those occurring in patients with other solid tumors who received Pembrolizumab as a single agent.

Immune-mediated adverse reactions, which may be severe or fatal, can occur with Pembrolizumab, including pneumonitis, colitis, hepatitis, endocrinopathies, nephritis and renal dysfunction, severe skin reactions, solid organ transplant rejection and complications of allogeneic hematopoietic stem cell transplantation ( HSCT ).
Based on the severity of the adverse reaction, Pembrolizumab should be withheld or discontinued and corticosteroids administered, if appropriate. can Pembrolizumab also cause severe or life-threatening infusion-related reactions.
Based on its mechanism of action, Pembrolizumab can cause fetal harm when administered to a pregnant woman.

Small cell lung cancer, which accounts for 10 to 15% of all lung cancers, is often diagnosed at an advanced stage where the prognosis is very poor and there have historically been limited treatment options. ( Xagena )

Source: Merck, 2019

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