Table I:

Key clinical trials of checkpoint inhibitors in metastatic and/or advanced breast cancer

Trial	Drug	Phase	Setting	Size	ORR	PFS	OS
KEYNOTE-012[37]	Pembrolizumab	Ib	Metastatic PD-L1+ TNBC	N = 27	19%	Median 1.9 mo.	Median 11.2 mo.
PANACEA/KEYNOTE-014[38]	Pembrolizumab	Ib/II	Progression on trastuzumab, HER2+	N = 52	15% (PD-L1+)	Median 2.7 mo. (PD-L1+)	NA
JAVELIN[39]	Avelumab	I	Metastatic	N = 168	3%; 17% (PD-L1+)	Median 5.9 mo.	Median 8.1 mo.
IMpassion[40]	Atezolizumab + nab-paclitaxel	III	Metastatic TNBC	N = 902	56%; 59% (PD-L1+)	Median 7.2 mo.	Median 25.0 mo.

ORR = objective response rate; PFS = progression-free survival; OS = overall survival; TNBC = triple-negative breast cancer; mo. = months.