A Study of Tucatinib Plus Trastuzumab Deruxtecan in HER2+ Breast Cancer

Confirmed objective response rate was defined as the percentage of participants with a confirmed complete response (CR) or partial response (PR) per investigator according to RECIST v1.1. For a response to be considered confirmed, the subsequent response had to be at least 4 weeks after the initial response. CR: disappearance of all target lesions and non-target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to less than (<)10 millimeters (mm). PR: a greater than equal to (>=) 30 percent (%) decrease in the sum of diameters of target lesions, taking as reference the baseline sum of diameters. 95% exact confidence interval (CI) was based on Clopper-Pearson method.

PFS as per INV was defined as the time from the start of the study treatment to the first documentation of PD per RECIST v1.1 or death due to 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 (this included the baseline sum if that was 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. The appearance of one or more new lesions was also considered progression. Kaplan-Meier methods was used for analysis.

DOR was defined as the time from the date of first documented objective response (CR or PR that was subsequently confirmed) to the date of first documented PD per RECIST v1.1 or death due to 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 (this included the baseline sum if that was 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. The appearance of one or more new lesions was also considered progression. CR: disappearance of all target lesions and non-target lesions. Any pathological lymph nodes (whether target or non-target) 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 of diameters. Kaplan-Meier methods was used for analysis.

DCR was defined as percentage of participants with confirmed CR, PR or stable disease ([SD] or non-CR/non-PD) per RECIST v1.1. CR: disappearance of all target lesions and non-target lesions. Any pathological lymph nodes (whether target or non-target) 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 of diameters. 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 included the baseline sum if that was 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. The appearance of one or more new lesions was also considered progression. 95% CI was computed using Clopper-Pearson method.

OS was defined as the time from the start of study treatment to the date of death due to any cause. Participants who were not known to have died at 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). For participants without data beyond the day of treatment initiation, OS was censored on the date of treatment initiation. Kaplan-Meier methods was used for analysis.

An adverse event (AE) was defined as any untoward medical occurrence in a clinical investigational participant administered a medicinal product which did not necessarily have a causal relationship with this treatment. AEs included all non-serious adverse events (non-SAEs) and SAEs. A TEAE was defined as a newly occurring or worsening AE after the first dose of study treatment (tucatinib or trastuzumab deruxtecan) and up through 30 days after the last dose of study treatment.

An SAE was an AE that at any dose, met any of the following criteria: resulted in death, was life-threatening, inpatient hospitalization or prolongation of existing hospitalization, persistent or significant incapacity or disability (substantial disruption of the participant's ability to conduct normal life functions), congenital anomaly/birth defect or considered medically significant.

An AE was defined was any untoward medical occurrence in a clinical investigational participant administered a medicinal product and which did not necessarily have a causal relationship with this treatment. A TEAE was defined as a newly occurring or worsening AE after the first dose of study treatment (tucatinib or trastuzumab deruxtecan) and up through 30 days after the last dose of study treatment. AEs were graded based on National Cancer Institute's Common Terminology Criteria for Adverse Events (NCI CTCAE), version 5.0 where, grade 1= mild; grade 2= moderate; grade 3= severe; grade 4= life-threatening; grade 5= death.

An AE was defined was any untoward medical occurrence in a clinical investigational participant administered a medicinal product and which did not necessarily have a causal relationship with this treatment. A TEAE was defined as a newly occurring or worsening AE after the first dose of study treatment (tucatinib or trastuzumab deruxtecan) and up through 30 days after the last dose of study treatment. Relatedness of AEs to study treatment was determined by the investigator.

Laboratory abnormalities included: hematology; hemoglobin increased and decreased, leukocytes decreased, lymphocytes increased and decreased, neutrophils decreased and platelets decreased. Chemistry: alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, creatinine, magnesium, potassium, sodium and total bilirubin increased and glucose, magnesium, potassium and sodium decreased. Treatment-emergent laboratory abnormalities were defined as abnormalities that are new or worsened on or after receiving the first dose of study treatment and up through 30 days after the last dose of study treatment. Laboratory test results were graded according to NCI CTCAE version 4.03, where Grade 0: no AE, Grade 1: mild AE; Grade 2: moderate AE; Grade 3: severe AE; Grade 4: life-threatening consequence, urgent intervention indicated; Grade 5: death related to AE. Number of participants with any grade are reported in this outcome measure.

An AE was defined was any untoward medical occurrence in a clinical investigational participant administered a medicinal product and which did not necessarily have a causal relationship with this treatment. A TEAE was defined as a newly occurring or worsening AE after the first dose of study treatment (tucatinib or trastuzumab deruxtecan) and up through 30 days after the last dose of study treatment. Dose modification included dose reduction, dose delay, dose hold and dose interruption. Number of participants with TEAEs leading to any type of dose modification for tucatinib and T-DXd are reported in this outcome measure.

An AE was defined was any untoward medical occurrence in a clinical investigational participant administered a medicinal product and which did not necessarily have a causal relationship with this treatment. A TEAE was defined as a newly occurring or worsening AE after the first dose of study treatment (tucatinib or trastuzumab deruxtecan) and up through 30 days after the last dose of study treatment. In this outcome measure, participants with TEAEs leading to discontinuation of tucatinib and T-DXd treatment is reported.

Cardiac ejection fraction was assessed using multiple-gated acquisition scan (MUGA) or echocardiogram (ECHO). Baseline was defined as most recent non-missing assessment on or before first dose date. Number of participants according to change from baseline in ejection fraction categories (i.e., no decrease, decrease <10%, decrease 10-<20% and decrease >=20%) is reported in this outcome measure.

Vital signs included body temperature, respiratory rate, heart rate, oxygen saturation, and systolic blood pressure (SBP) and diastolic blood pressure (DBP). The clinically significant vital signs were defined as: heart rate > 100 beats per minute (bpm), temperature >=38.0 degrees Celsius (C), respiratory rate > 20 breaths per minute and oxygen saturation < 88%; SBP >=120 millimeters of mercury (mmHg) or DBP >=80 mmHg; SBP >=140 mmHg or DBP >=90 mmHg and SBP >=160 mmHg or DBP>=100 mmHg.