All Cohort A Dose Escalation Participants:\r\n* Prior hormonal therapy: Participants may have received any number of previous endocrine / hormonal lines of therapy in the metastatic setting (including prior fulvestrant), as long as the last dose is >= 14 days prior to first dose of study treatment\r\n* Prior biologics / investigational therapy: Prior therapy with biologics and investigational drugs is allowed, as long as the last dose is >= 21 days prior to first dose of study treatment\r\n* Prior CDK4/6 inhibition is allowed; participants who have had prior ribociclib must have received treatment at full-dose without any dose reductions; the last dose is required to be >= 21 days prior to first dose of study treatment\r\n* Treatment with prior PD1/PDL1/CTLA4 inhibitors is prohibited\r\n* Prior radiotherapy: Participants may have received radiotherapy for palliative purposes but must have completed treatment ? 14 days prior to first dose of study treatment and not be experiencing grade > 1 treatment-related toxicities\r\n* Evaluable or measurable disease by RECIST 1.1
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Hormone receptor (HR)-positive, HER2-negative metastatic breast cancer according to ASCO CAP guidelines
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Men are eligible, as long as on a GnRH agonist for at least 6 weeks prior to study entry; men MUST remain on the GnRH agonist for the duration of protocol treatment
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Evaluable or measurable disease by RECIST 1.1
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Prior CDK4/6 inhibition is allowed; participants who have had prior ribociclib must have received treatment at full-dose without any dose-reductions; the last dose is required to be >= 21 days prior to first study treatment
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Treatment with prior PD1/PDL1/CTLA4 inhibitors is prohibited
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Prior hormonal therapy: \r\n* Participants may have received any number of previous endocrine / hormonal lines of therapy (including prior fulvestrant) in the metastatic setting, as long as the last dose is >= 14 days prior to first dose of study treatment
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Prior chemotherapy:\r\n* Participants may have received chemotherapy for advanced breast cancer as long as the last dose is >= 21 days prior to registration
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Prior biologics / investigational therapy: \r\n* Prior therapy with biologics and investigational drugs is allowed, as long as the last dose is >= 21 days prior to first dose of study treatment
Cohort B Safety Run-In (Ribociclib + PDR001 + Fulvestrant): Prior radiotherapy;\r\n* Participants may have received radiotherapy for palliative purposes but must have completed treatment >= 14 days prior to first dose of study treatment and not be experiencing > grade 1 treatment related toxicities
Cohort A Dose Expansion (Ribociclib + PDR001): Prior hormonal therapy: \r\n* Participants may have received any number of previous endocrine / hormonal lines of therapy in the metastatic setting, as long as the last dose is >= 14 days prior to first dose of study treatment
Cohort A Dose Expansion (Ribociclib + PDR001): Prior biologics / investigational therapy: \r\n* Prior therapy with biologics and investigational drugs is allowed, as long as the last dose is >= 21 days prior to first dose of study treatment
Cohort A Dose Expansion (Ribociclib + PDR001): Prior radiotherapy: \r\n* Participants may have received radiotherapy for palliative purposes but must have completed treatment >= 14 days prior to first dose of study treatment and not be experiencing grade > 1 treatment-related toxicities
Cohort A Dose Expansion (Ribociclib + PDR001): Treatment with prior CDK4/6 inhibitors is prohibited
Cohort A Dose Expansion (Ribociclib + PDR001): Treatment with prior PD1/PDL1/CTLA4 is prohibited
Cohort A Dose Expansion (Ribociclib + PDR001): Measurable disease by RECIST 1.1 is required
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Hormone receptor (HR)-positive, HER2-negative metastatic breast cancer according to ASCO CAP guidelines
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Men are eligible, as long as on a GnRH agonist for at least 6 weeks prior to study entry; men MUST remain on the GnRH agonist for the duration of protocol treatment
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Prior hormonal therapy:\r\n* Participants may have received any number of previous endocrine / hormonal lines of therapy in the metastatic setting, as long as the last dose is >= 14 days prior to first dose of study treatment\r\n* Participants must have progressed on an aromatase inhibitor in the metastatic setting or experienced disease recurrence within 6 months of completing adjuvant therapy with an aromatase inhibitor\r\n* Treatment with prior fulvestrant is prohibited
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Prior chemotherapy:\r\n* Participants may have received up to one prior line of chemotherapy for advanced breast cancer as long as the last dose is >= 21 days prior to first dose of study treatment
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Prior biologics / investigational therapy:\r\n* Prior therapy with biologics and investigational drugs is allowed, as long as the last dose is >= 21 days prior to first dose of study treatment
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Prior radiotherapy:\r\n* Participants may have received radiotherapy for palliative purposes but must have completed treatment >= 14 days prior to first dose of study treatment and not be experiencing grade > 1 treatment-related toxicities
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Treatment with prior CDK4/6 inhibitors are prohibited
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Treatment with prior PD1/PDL1/CTLA4 inhibitors are prohibited
Expansion Cohort B (Ribociclib + PDR001 + Fulvestrant): Measurable disease by RECIST 1.1 is required
Has completed prior therapies according to the criteria below:\r\n* Cytotoxic chemotherapy - at least 21 days since last dose prior to first dose of ribociclib\r\n* Small molecule inhibitors - at least 14 days since last dose prior to first dose of ribociclib\r\n* Monoclonal antibodies - at least 3 half-lives since last dose prior to first dose of ribociclib; exception: denosumab for bony metastases is allowable\r\n* Immunotherapy (e.g. tumor vaccines) - at least 42 days since last dose prior to first dose of ribociclib\r\n* Radiation - at least 14 days since last dose prior to first dose of ribociclib