Levels of Circulating Tumor DNA as a Predictive Marker for Early Switch in Treatment for Patients With Metastatic (Stage IV) Breast Cancer

"Participants will receive standard of care one of three available AI therapies in combination with one of three available CDK4/6i therapies:~* AI: Anastrozole, Letrozole or Exemestane~* CDK4/6i: Palbociclib, Ribociclib or Abemaciclib"

"Participants will receive standard of care SERD therapy in the form of Fulvestrant, in combination with one of three one of three available CDK4/6i therapies:~* SERD: Fulvestrant~* CDK4/6i: Palbociclib, Ribociclib or Abemaciclib"

Participants will receive standard of care mTOR inhibitor therapy (Everolimus) in combination with AI therapy (Exemestane) in Step 2 Arm 2 and Step 3. mTOR inhibitor + AI therapy administered as one of the available options for early switch from AI+CDK4/6i or SERD+CDk4/6i therapy in administered in Step 1.

Participants will receive standard of care mTOR inhibitor therapy (Everolimus) in combination with SERD therapy (Fulvestrant), in Step 2 Arm 2 and Step 3. mTOR inhibitor + SERD therapy administered as one of the available options for early switch from AI+CDK4/6i or SERD+CDk4/6i therapy in administered in Step 1.

Participants will receive standard of care mTOR inhibitor therapy (Everolimus) in combination with selective estrogen receptor modulator therapy (Tamoxifen) in Step 2 Arm 2 and Step 3. mTOR inhibitor + Selective estrogen receptor modulator therapy administered as one of the available options for early switch from AI+CDK4/6i or SERD+CDk4/6i therapy in administered in Step 1.

Participants will receive standard of care one PI3K inhibitor therapy (Alpelisib), in combination with SERD therapy (Fulvestrant) in Step 2 Arm 2 and Step 3. PI3K inhibitor + SERD therapy administered as one of the available options for early switch from AI+CDK4/6i or SERD+CDk4/6i therapy in administered in Step 1.

Participants will receive standard of care a PI3K inhibitor therapy (Alpelisib), in combination with an AI therapy (Letrozole) in Step 2 Arm 2 and Step 3. PI3K inhibitor + AI therapy administered as one of the available options for early switch from SERD+CDk4/6i therapy in administered in Step 1.

Chemotherapy administered standard of care as an alternative therapy in Step 2 Arm 2 and Step 3.

Participants will receive standard of care oral SERD therapy (Elacestrant) in Step 2 Arm 2 and Step 3. Oral SERD therapy administered as one of the available options for early switch from AI+CDK4/6i or SERD+CDk4/6i therapy in administered in Step 1.

For participants with germline breast cancer gene (BRCA) mutation(s). Participants will receive standard of care PARPi (Olaparib or Talazoparib) therapy in Step 2 and Step 3.

For participants with tumors with one or more phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) or AKT serine/threonine kinase 1 (AKT1) or phosphatase and tensin homolog (PTEN) alterations. Participants in Step 2 and Step 3 will receive standard of care AKT inhibitor as an alternative therapy.

Participants will receive third-line treatment standard of care as per their treating physician's choice according to National Comprehensive Cancer Network (NCCN) guidelines.