A Study of Tucatinib vs. Placebo in Combination With Ado-trastuzumab Emtansine (T-DM1) for Patients With Advanced or Metastatic HER2+ Breast Cancer

OS was defined as the time from randomization to death due to any cause. For a participant who was not known to have died by the end of study follow-up, observation of OS was censored on the date the participant was last known to be alive (i.e., the date of last contact).

PFS as per investigator was defined as the time from the date of randomization to the investigator assessment of PD as per RECIST v1.1 or death from any cause, whichever occurred first. PD: at least a 20 % increase in the sum of diameters of target lesions, taking as reference the smallest sum on study. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. Participants without documentation of PD, or death at the time of analysis were censored at the date of the last tumor assessment. PFS was analyzed in participants with presence or history of brain metastases.

ORR was defined as the percentage of participants with confirmed complete response (CR) or partial response (PR) according to RECIST v1.1. CR: disappearance of all target lesions. Any pathological lymph nodes must have reduction in short axis to less than (\<)10 mm. PR: a greater than equal (\>=) 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. For a response to be considered as confirmed, the subsequent response needs to be at least 4 weeks after the initial response. ORR by investigator assessment is based on investigator response assessments. Two-sided 95% exact confidence interval, computed using the Clopper-Pearson method.

OS was defined as the time from randomization to death due to any cause. For a participant who was not known to have died by the end of study follow-up, observation of OS was censored on the date the participant was last known to be alive (i.e., the date of last contact). OS was analyzed in participants with presence or history of brain metastases.

PFS as per BICR was defined as the time from the date of randomization to the centrally-reviewed documented PD as per RECIST v1.1 or death from any cause, whichever occurred first. PD: at least a 20 % increase in the sum of diameters of target lesions, taking as reference the smallest sum on study. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. Participants without documented progression of PD or death at the time of analysis were censored at the date of the last tumor assessment.

PFS as per BICR was defined as the time from the date of randomization to the centrally-reviewed documented PD as per RECIST v1.1 or death from any cause, whichever occurred first. PD: at least a 20 % increase in the sum of diameters of target lesions, taking as reference the smallest sum on study. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. PFS was analyzed in participants with presence or history of brain metastases.

ORR was defined as the percentage of participants with confirmed CR or PR according to RECIST v1.1. CR: Disappearance of all target lesions. Any pathological lymph nodes must have reduction in short axis to \<10 mm. PR: A \>= 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. ORR per BICR is based on BICR response assessments.

DOR was defined as the time from first documentation of objective response (CR or PR that is subsequently confirmed) to the first documentation of PD as per RECIST v1.1 PD: at least a 20 % increase in the sum of diameters of target lesions, taking as reference the smallest sum on study. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. Participants without documentation of PD, or death at the time of analysis were censored at the date of the last tumor assessment. CR: disappearance of all target lesions. Any pathological lymph nodes must have reduction in short axis to \<10 mm. PR: A\>=30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. DOR per investigator was based on investigator response assessments.

DOR was defined as the time from first documentation of objective response (CR or PR that is subsequently confirmed) to the first documentation of PD as per RECIST v1.1 PD: at least a 20 % increase in the sum of diameters of target lesions, taking as reference the smallest sum on study. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. Participants without documentation of PD, or death at the time of analysis were censored at the date of the last tumor assessment. CR: disappearance of all target lesions. Any pathological lymph nodes must have reduction in short axis to \<10 mm. PR: A\>=30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. DOR per BICR was based on BICR response assessments.

CBR was defined as the percentage of participants with stable disease (SD) or non-CR or non-PD \>= 6 months or best response of CR or PR according to RECIST v1.1. SD: neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study. PD: at least a 20% increase in the sum of diameters of target lesions, taking as reference the smallest sum on study (this includes the baseline sum if that is the smallest on study). In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. CR: disappearance of all target lesions. Any pathological lymph nodes must have reduction in short axis to \<10 mm. PR: A \>= 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. CBR was based on investigator assessment.