A Phase 1a/1b Study of BG-68501, a Selective CDK2 Inhibitor, in Participants With Advanced Solid Tumors

• BG-68501 is a CDK2 Inhibitor

In this study, the sponsor and investigators want to learn:

• How much of the study drug can be given with an acceptable level of side effects
• The effects of the study drug (good and bad) alone and in combination with Fulvestrant
• How much of the study drug is absorbed into the blood and how fast it is removed
• How the study drug is acting on your body

You will receive one of the study regimen options:
• Part A Monotherapy: If you are assigned to this group, you will receive BG-68501 (single drug), as per instructions below.

• Part B Combination Therapy: If you are assigned to this group, you will receive BG-68501 in combination with Fulvestrant.

• Safety Expansion (Either Monotherapy or Combination Therapy): If you are assigned to this group, you will receive BG-68501 (single drug) or BG-68501 in combination with Fulvestrant.

This is a dose escalation study. Dose Escalation means that the amount of the study drug given will be increased in each group of research participants, to find the most appropriate dose for further study.

Your study doctor together with the study sponsor will decide on the dose level of study drug given to you.

The study regimen will be given in cycles. Each cycle is 28 days. You will receive the study drug twice a day by mouth. If you are taking part in the combination arms, you will receive the study drug by mouth twice a day and Fulvestrant injections on Days 1 and 15 of Cycle 1, and Day 1 of every other cycle.

If you are in the Safety Expansion Group, you may be required to have paired biopsies, meaning a fresh biopsy before you receive the study regimen and another after you start the study regimen.