Due to the high expression of PD-L1 in endometrial cancers as well as in ovarian cancers
which are molecularly similar to uterine serous cancers, using pembrolizumab should be
beneficial in this patient population. Since the investigators are able to get a
pre-treatment research- related endometrial biopsy as well as the surgical specimen post two
cycles of pembrolizumab, the investigators will be able to evaluate the mechanism of action
of this drug on the endometrial cancer tumor environment.