This is a multicenter, Phase 1b/2 trial. The phase 1b part of the trial aims to determine the
RP2D of elacestrant when administered in combination with alpelisib, everolimus, palbociclib,
and ribociclib. The Phase 2 part of the trial will evaluate the efficacy and safety of the
various combinations in patients with ER+/HER2- advanced/metastatic breast cancer.

This is a Phase 1b open-label, 2-part study in 2 treatment groups. The 2 treatment groups are
as follows:

Treatment Group 1: OP-1250 in combination with ribociclib (KISQALI, Novartis Pharmaceuticals
Corporation).

Treatment Group 2: OP-1250 in combination with alpelisib (PIQRAY, Novartis Pharmaceuticals
Corporation).