Study of Pembrolizumab in Metastatic HER2-negative Breast Cancer Patients With APOBEC3B Mutation

"The planned dose of pembrolizumab for this study is 200 mg every 3 weeks (Q3W). Based on the totality of data generated in the Keytruda® development program, 200 mg Q3W is the appropriate dose of pembrolizumab for adults across all indications and regardless of tumour type.~All participants who off study treatment with stable disease (SD) or better may be eligible for up to an additional 17 cycles (approximately 1 year) of pembrolizumab treatment if they progress after stopping study treatment from the initial treatment phase. This retreatment is termed the Second Course Phase of this study and is only available if the study remains open and the participant met certain criteria as stated in the protocol."