A Study of Pembrolizumab (MK-3475) Versus Paclitaxel for Participants With Advanced Gastric/Gastroesophageal Junction Adenocarcinoma That Progressed After Therapy With Platinum and Fluoropyrimidine (MK-3475-061/KEYNOTE-061)

PFS According to RECIST 1.1 Based on BICR in All Participants

PFS was defined as the time from randomization to the first documented disease progression per RECIST 1.1 based on BICR, or death due to any cause, whichever occurs first. According to RECIST 1.1, PD was defined as a 20% relative increase in the SOD of target lesions, taking as reference the nadir SOD and an absolute increase of \>5 mm in the SOD, or the appearance of new lesions. PFS was analyzed using the Kaplan-Meier method and median PFS (95% CI) in months was reported for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

OS in All Participants

OS was defined as the time from randomization to death due to any cause. Participants without documented death at the time of the final analysis were censored at the date of the last follow-up. OS was analyzed using the Kaplan-Meier method and median OS (95% CI) in months was reported for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

PFS According to RECIST 1.1 Based on Investigator Assessment in PD-L1 Positive Participants

PFS was defined as the time from randomization to the first documented disease progression per RECIST 1.1 based on investigator assessment, or death due to any cause, whichever occurs first. According to RECIST 1.1, PD was defined as a 20% relative increase in the SOD of target lesions, taking as reference the nadir SOD and an absolute increase of \>5 mm in the SOD, or the appearance of new lesions. PFS was analyzed using the Kaplan-Meier method and median PFS (95% CI) in months was reported for PD-L1 positive participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

PFS According to RECIST 1.1 Based on Investigator Assessment in All Participants

PFS was defined as the time from randomization to the first documented disease progression per RECIST 1.1 based on investigator assessment, or death due to any cause, whichever occurs first. According to RECIST 1.1, PD was defined as a 20% relative increase in the SOD of target lesions, taking as reference the nadir SOD and an absolute increase of \>5 mm in the SOD, or the appearance of new lesions. PFS was analyzed using the Kaplan-Meier method and median PFS (95% CI) in months was reported for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

PFS According to Immune-Related Response Evaluation Criteria in Solid Tumors (irRECIST) Based on BICR in PD-L1 Positive Participants

PFS defined as time from randomization to first documented PD per irRECIST based on BICR, or death due to any cause, whichever occurs first. Following initial PD by RECIST 1.1 (20% relative increase in SOD of target lesions), participants were assessed according to irRECIST: tumor assessment was repeated ≥4 weeks later to confirm PD with the option of continuing treatment until this scan was obtained for clinically stable participants. If PD confirmed, participant was discontinued from treatment unless investigator determined benefit. If repeat scan indicated stable disease (SD; neither sufficient shrinkage or increase of target lesion), partial response (PR; ≥30% decrease in the SOD of target lesions), or complete response (CR; disappearance of all non-nodal target lesions), participant could continue treatment at investigator's discretion. PFS analyzed using Kaplan-Meier method and median PFS (95% CI) in months was reported for PD-L1 positive participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

PFS According to irRECIST Based on BICR in All Participants

PFS defined as time from randomization to first documented PD per irRECIST based on BICR, or death due to any cause, whichever occurs first. Following initial PD by RECIST 1.1 (20% relative increase in SOD of target lesions), participants were assessed according to irRECIST: tumor assessment was repeated ≥4 weeks later to confirm PD with the option of continuing treatment until this scan was obtained for clinically stable participants. If PD confirmed, participant was discontinued from treatment unless investigator determined benefit. If repeat scan indicated SD (neither sufficient shrinkage or increase of target lesion), PR (≥30% decrease in the SOD of target lesions), or CR (disappearance of all non-nodal target lesions), participant could continue treatment at investigator's discretion. PFS analyzed using Kaplan-Meier method and median PFS (95% CI) in months was reported for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

Time to Tumor Progression (TTP) According to RECIST 1.1 Based on BICR in PD-L1 Positive Participants

TTP was defined as the time from randomization to the first documented disease progression per RECIST 1.1 based on BICR. Using RECIST 1.1, progressive disease was defined as a 20% relative increase in the SOD of target lesions, taking as reference the nadir SOD and an absolute increase of \>5 mm in the SOD, or the appearance of new lesions. If there was no documented disease progression, TTP was censored at last tumor assessment date. TTP was analyzed using the Kaplan-Meier method and median TTP (95% CI) in months was reported for PD-L1 positive participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

TTP According to RECIST 1.1 Based on BICR in All Participants

TTP was defined as the time from randomization to the first documented disease progression per RECIST 1.1 based on BICR. Using RECIST 1.1, progressive disease was defined as a 20% relative increase in the SOD of target lesions, taking as reference the nadir SOD and an absolute increase of \>5 mm in the SOD, or the appearance of new lesions. If there was no documented disease progression, TTP was censored at last tumor assessment date. TTP was analyzed using the Kaplan-Meier method and median TTP (95% CI) in months was reported for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

TTP According to RECIST 1.1 Based on Investigator Assessment in PD-L1 Positive Participants

TTP was defined as the time from randomization to the first documented disease progression per RECIST 1.1 based on investigator assessment. Using RECIST 1.1, progressive disease was defined as a 20% relative increase in the SOD of target lesions, taking as reference the nadir SOD and an absolute increase of \>5 mm in the SOD, or the appearance of new lesions. If there was no documented disease progression, TTP was censored at last tumor assessment date. TTP was analyzed using the Kaplan-Meier method and median TTP (95% CI) in months was reported for PD-L1 positive participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

TTP According to RECIST 1.1 Based on Investigator Assessment in All Participants

TTP was defined as the time from randomization to the first documented disease progression per RECIST 1.1 based on investigator assessment. Using RECIST 1.1, progressive disease was defined as a 20% relative increase in the SOD of target lesions, taking as reference the nadir SOD and an absolute increase of \>5 mm in the SOD, or the appearance of new lesions. If there was no documented disease progression, TTP was censored at last tumor assessment date. TTP was analyzed using the Kaplan-Meier method and median TTP (95% CI) in months was reported for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

Objective Response Rate (ORR) According to RECIST 1.1 Based on BICR in PD-L1 Positive Participants

ORR was defined as the percentage of the participants in the analysis population who had a confirmed CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on BICR. ORR was analyzed using the stratified Miettinen and Nurminen method, and reported with 95% CI for PD-L1 positive participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

ORR According to RECIST 1.1 Based on BICR in All Participants

ORR was defined as the percentage of the participants in the analysis population who had a confirmed CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on BICR. ORR was analyzed using the stratified Miettinen and Nurminen method, and reported with 95% CI for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

ORR According to RECIST 1.1 Based on Investigator Assessment in PD-L1 Positive Participants

ORR was defined as the percentage of the participants in the analysis population who had a confirmed CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on investigator assessment. ORR was analyzed using the stratified Miettinen and Nurminen method, and reported with 95% CI for PD-L1 positive participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

ORR According to RECIST 1.1 Based on Investigator Assessment in All Participants

ORR was defined as the percentage of the participants in the analysis population who had a confirmed CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on investigator assessment. ORR was analyzed using the stratified Miettinen and Nurminen method, and reported with 95% CI for all participants by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

Duration of Response (DOR) According to RECIST 1.1 Based on BICR in PD-L1 Positive Participants

For PD-L1 positive participants who demonstrated CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on BICR, DOR was defined as the time from first documented evidence of CR or PR until disease progression or death due to any cause, whichever occurs first. DOR for participants who had not progressed or died at the time of analysis was censored at the date of their last tumor assessment. DOR was analyzed using the Kaplan-Meier method and median DOR (range) in months was reported for PD-L1 positive participants with response by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

DOR According to RECIST 1.1 Based on BICR in All Participants

For participants who demonstrated CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on BICR, DOR was defined as the time from first documented evidence of CR or PR until disease progression or death due to any cause, whichever occurs first. DOR for participants who had not progressed or died at the time of analysis was censored at the date of their last tumor assessment. DOR was analyzed using the Kaplan-Meier method and median DOR (range) in months was reported for all participants with response by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

DOR According to RECIST 1.1 Based on Investigator Assessment in PD-L1 Positive Participants

For PD-L1 positive participants who demonstrated CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on investigator assessment, DOR was defined as the time from first documented evidence of CR or PR until disease progression or death due to any cause, whichever occurs first. DOR for participants who had not progressed or died at the time of analysis was censored at the date of their last tumor assessment. DOR was analyzed using the Kaplan-Meier method and median DOR (range) in months was reported for PD-L1 positive participants with response by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

DOR According to RECIST 1.1 Based on Investigator Assessment in All Participants

For participants who demonstrated CR (disappearance of all non-nodal target lesions and any pathological lymph nodes must have become normal) or PR (at least a 30% decrease in the SOD of target lesions, taking as reference the baseline SOD) according to RECIST 1.1 and based on investigator assessment, DOR was defined as the time from first documented evidence of CR or PR until disease progression or death due to any cause, whichever occurs first. DOR for participants who had not progressed or died at the time of analysis was censored at the date of their last tumor assessment. DOR was analyzed using the Kaplan-Meier method and median DOR (range) in months was reported for all participants with response by treatment group.

Time frame: Up to 30 months (through database cut-off date of 26 Oct 2017)

Percentage of PD-L1 Positive Participants Who Experienced an Adverse Event (AE)

An AE was defined as any untoward medical occurrence in a participant administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment. An AE could therefore be any unfavourable and unintended sign, symptom, or disease temporally associated with the use of a medicinal product or protocol-specified procedure, whether or not considered related to the medicinal product or protocol-specified procedure. Any worsening of a pre-existing condition that was temporally associated with the use of the Sponsor's product was also an AE. The percentage of participants with at least one AE was reported for PD-L1 positive participants by treatment group.

Time frame: Up to 71 months (through database cut-off date of 10 Jun 2021)

Percentage of All Participants Who Experienced an AE

An AE was defined as any untoward medical occurrence in a participant administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment. An AE could therefore be any unfavourable and unintended sign, symptom, or disease temporally associated with the use of a medicinal product or protocol-specified procedure, whether or not considered related to the medicinal product or protocol-specified procedure. Any worsening of a pre-existing condition that was temporally associated with the use of the Sponsor's product was also an AE. The percentage of participants with at least one AE was reported for all participants by treatment group.

Time frame: Up to 71 months (through database cut-off date of 10 Jun 2021)

Percentage of PD-L1 Positive Participants That Discontinued Study Treatment Due to AE

An AE was defined as any untoward medical occurrence in a participant administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment. An AE could therefore be any unfavourable and unintended sign, symptom, or disease temporally associated with the use of a medicinal product or protocol-specified procedure, whether or not considered related to the medicinal product or protocol-specified procedure. Any worsening of a pre-existing condition that was temporally associated with the use of the Sponsor's product was also an AE. The percentage of participants that discontinued study treatment due to an AE was reported for PD-L1 positive participants by treatment group.

Time frame: Up to approximately 26.4 months

Percentage of All Participants That Discontinued Study Treatment Due to AE

An AE was defined as any untoward medical occurrence in a participant administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment. An AE could therefore be any unfavourable and unintended sign, symptom, or disease temporally associated with the use of a medicinal product or protocol-specified procedure, whether or not considered related to the medicinal product or protocol-specified procedure. Any worsening of a pre-existing condition that was temporally associated with the use of the Sponsor's product was also an AE. The percentage of participants that discontinued study treatment due to an AE was reported for all participants by treatment group.

Time frame: Up to approximately 26.4 months