A Study to Evaluate the Effect of GDC-4198 Alone and in Combination With Giredestrant Versus Abemaciclib and Giredestrant in Participants With Locally Advanced or Metastatic Estrogen Receptor-Positive (ER+), Human Epidermal Growth Factor Receptor-Negative (HER2-) Breast Cancer

Exclusion Criteria

• •Advanced, symptomatic, visceral spread that is at risk of life-threatening complications in the short term appropriate for treatment with cytotoxic chemotherapy at time of entry into the study, as per national or local treatment guidelines.
• •Have received more than one-line of therapy for locally advanced or metastatic disease.
• •Have received prior chemotherapy for metastatic breast cancer
• •Treatment with anti-cancer therapies, including investigational therapies, within 28 days or 5 drug elimination half -lives, whichever is shorter, prior to initiation of study drug. Treatment with an approved oral endocrine therapy (ET) within 7 days prior to initiation of study drug; treatment with fulvestrant or an approved CDK4/6 inhibitor within 21 days prior to initiation of study drug.
• •Poor peripheral venous access
• •Malabsorption condition or other gastrointestinal (GI) conditions/surgeries that the investigator assesses may significantly interfere with enteral absorption
• •History of malignancy within 3 years prior to screening, except for cancer under investigation in this study and malignancies with a negligible risk of metastasis or death.