A Phase 3 interventional study of LY4064809 and Placebo in Breast Neoplasms and Neoplasm Metastasis, sponsored by Eli Lilly and Company. Recruiting at 364 sites in 19 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-11-04.
Sponsored by Eli Lilly and Company · Phase 3, Interventional, and Treatment
The purpose of the study is to assess the efficacy and safety of the addition of Tersolisib (LY4064809/STX-478) to other anti-cancer drugs as first treatment for advanced hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer. Participants can remain in the study as long as the drug is helping the cancer without unbearable side effects.
14,825 studies on the registry are indexed under Breast Neoplasms; 3,319 are open to participants now.
This study's planned enrollment of 800 is above the median of 72 across 10,896 interventional studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →Eli Lilly and Company is the lead sponsor of 2,106 studies on the registry; 152 are open to participants now.
Of its 536 completed or terminated interventional studies of FDA-regulated products, 357 (67%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Have or cytologically confirmed breast cancer, defined as individuals with
hormone receptors (HR)+/human epidermal growth factor receptor 2 ()- or HR+/HER low defined by American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) Guidelines
Part 1:
Part 2:
Individuals who are eligible are either
Population 1 (P1): Endocrine sensitive
Population 2 (P2): Endocrine resistant
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Periods have stopped for good: usually no period for 12 months in a row without another medical reason, sometimes confirmed by a blood test (FSH).
The diagnosis was confirmed by looking at a sample under a microscope: tissue from a biopsy or surgery (histology), or cells from a fluid or needle sample (cytology).
Your pathology report is the document that shows this.
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
A biopsy takes a small piece of tissue to examine. “Archival tissue” is a sample already taken, for example at diagnosis, and kept by the hospital.
Whether a stored sample will do depends on when it was taken, how much there is and what the study needs. Ask whether the study accepts your stored sample or needs a new biopsy.
The amount of disease can be tracked with a defined measurement, so the study can see whether it shrinks or grows. It might be a tumour measured on a scan or, in some blood cancers such as myeloma, a marker measured in blood or urine.
The criteria or the study team say which measurement counts — having no tumour visible on a scan does not by itself rule you out.
Relapsed: the illness came back after treatment had worked. Refractory: it did not respond to treatment, or stopped responding while still on it.
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
A blood test of average blood sugar over the past two to three months, given as a percentage or in mmol/mol. 6.5% (48 mmol/mol) or more is the usual threshold for diabetes, normally confirmed by a second test.
Cancer that has spread to the leptomeninges, the thin layers covering the brain and spinal cord, and the fluid between them. It is not the same as brain metastases.
Criteria often treat it separately, and many studies leave it out even where treated brain metastases are allowed.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
A planned gap after a treatment, so that its effects can lessen before the study treatment or a study assessment. Ask the study team and the doctor who prescribed it before changing any medicine.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Postmenopausal
Periods have stopped for good: usually no period for 12 months in a row without another medical reason, sometimes confirmed by a blood test (FSH).
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Histologically or cytologically confirmed
The diagnosis was confirmed by looking at a sample under a microscope: tissue from a biopsy or surgery (histology), or cells from a fluid or needle sample (cytology).
Your pathology report is the document that shows this.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Metastases
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HER2
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Biopsy and archival tissue
A biopsy takes a small piece of tissue to examine. “Archival tissue” is a sample already taken, for example at diagnosis, and kept by the hospital.
Whether a stored sample will do depends on when it was taken, how much there is and what the study needs. Ask whether the study accepts your stored sample or needs a new biopsy.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Measurable disease
The amount of disease can be tracked with a defined measurement, so the study can see whether it shrinks or grows. It might be a tumour measured on a scan or, in some blood cancers such as myeloma, a marker measured in blood or urine.
The criteria or the study team say which measurement counts — having no tumour visible on a scan does not by itself rule you out.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Relapsed and refractory
Relapsed: the illness came back after treatment had worked. Refractory: it did not respond to treatment, or stopped responding while still on it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Adjuvant and neoadjuvant
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HbA1c
A blood test of average blood sugar over the past two to three months, given as a percentage or in mmol/mol. 6.5% (48 mmol/mol) or more is the usual threshold for diabetes, normally confirmed by a second test.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Leptomeningeal disease
Cancer that has spread to the leptomeninges, the thin layers covering the brain and spinal cord, and the fluid between them. It is not the same as brain metastases.
Criteria often treat it separately, and many studies leave it out even where treated brain metastases are allowed.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Washout period
A planned gap after a treatment, so that its effects can lessen before the study treatment or a study assessment. Ask the study team and the doctor who prescribed it before changing any medicine.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
LY4064809 given orally in one of two doses in combination with investigator's choice of CDK4/6 inhibitor given orally and ET given orally or intramuscularly
Drug: LY4064809 · Drug: Ribociclib · Drug: Palbociclib · Drug: Abemaciclib · Drug: Anastrozole · Drug: Letrozole · Drug: Exemestane · Drug: Fulvestrant
LY4064809 given orally in combination with CDK4/6 inhibitor given orally and ET given orally or intramuscularly
Drug: LY4064809 · Drug: Ribociclib · Drug: Palbociclib · Drug: Abemaciclib · Drug: Anastrozole · Drug: Letrozole · Drug: Exemestane · Drug: Fulvestrant
Placebo given orally in combination with CDK4/6 inhibitor given orally and ET given orally or intramuscularly
Drug: Placebo · Drug: Ribociclib · Drug: Palbociclib · Drug: Abemaciclib · Drug: Anastrozole · Drug: Letrozole · Drug: Exemestane · Drug: Fulvestrant
Administered orally
Also known as: STX-478, Tersolisib
Administered orally
Administered orally
Administered orally
Administered orally
Also known as: LY2835219
Administered orally
Administered orally
Administered orally
Administered intramuscular
(Part 1): Overall Response Rate (ORR): Percentage of Participants with Confirmed Complete Response (CR) or Partial Response (PR)
As determined by the investigator based on Response Evaluation Criteria in Solid Tumors (RECIST) v 1.1
Time frame: Baseline through disease progression or death (Estimated up to 5 years)
(Part 2): Progression-Free Survival
Investigator-assessed
Time frame: Baseline to objective progression or death due to any cause (Estimated up to 5 years)
(Part 1): Disease Control Rate (DCR)
per RECIST v1.1
Time frame: Baseline through measured progressive disease (Estimated up to 5 years)
(Part 1): Time to Response (TTR)
per RECIST v1.1
Time frame: Baseline until the date that measurement criteria for CR or PR (whichever is first recorded) are first met (Estimated as approximately 5 years)
(Parts 1 and 2): Duration of Response (DOR)
per RECIST v1.1
Time frame: Date of CR or PR to date of objective disease progression or death due to any cause (Estimated up to 5 years)
(Part 1): PFS
per RECIST v1.1
Time frame: Baseline to objective progression or death due to any cause (Estimated up to 5 years)
(Parts 1 and 2): Overall Survival (OS)
Time frame: Baseline to deaths from any cause (Estimated up to 7 years)
(Parts 1 and 2): Clinical Benefit Rate (CBR): Percentage of Participants with a BOR of CR or PR, or SD Lasting Greater than or Equal to Six Months
per RECIST v1.1
Time frame: Baseline to disease progression or death from any cause (Estimated up to 5 years)
(Parts 1 and 2): PK: Average Plasma Concentrations of tersolisib
Time frame: Baseline to last PK sample collection up to 5 months
(Part 2): Progression-Free Survival after Subsequent Line of Treatment (PFS2)
Investigator-assessed
Time frame: Baseline to disease progression on next line of treatment or death from any cause (Estimated as up to 7 years)
(Part 2): Progression-Free Survival (PFS)
By BICR
Time frame: Baseline to objective progression or death from any cause (Estimated up to 5 years)
(Part 2): Objective Response Rate (ORR)
By investigator and blinded independent central review (BICR)
Time frame: Baseline to disease progression or death from any cause (Estimated up to 5 years)
(Part 2): Time to Chemotherapy (TTC)
Time frame: Baseline until the start of chemotherapy (Estimated up to 7 years)
(Part 2): Chemotherapy-Free Survival
Time frame: Baseline until the start of chemotherapy or death from any cause (Estimated up to 7 years)
(Part 2): Change in Overall Health-related Quality of Life (HRQoL) as measured by European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30) Global Health Status/Quality of Life Subscale
The EORTC QLQ-C30 is a 30-question patient-reported instrument used to assess multidimensional HRQoL in cancer patients. Overall HRQoL is measured by the EORTC QLQ-C30 Global Health Status/Quality of Life Subscale (two items). Response options range from 1) "very poor" to 7) "excellent." Score is linearly transformed to the range 0 - 100. Higher score represents better overall HRQoL.
Time frame: Baseline until disease progression or death (Estimated up to 7 years)
(Part 2): Change in Physical Function as measured by the EORTC QLQ-C30 Physical Functioning Subscale
The EORTC QLQ-C30 is a 30-question patient-reported instrument used to assess multidimensional HRQoL in cancer patients. Physical function is measured by the EORTC QLQ-C30 Physical Functioning subscale (five items). Response options range from 1) "not at all" to 4) "very much." Score is linearly transformed to the range 0 - 100. Higher score represents better overall physical function.
Time frame: Baseline until disease progression or death (Estimated up to 7 years)
Not enrolling at this site — choose another above.
Showing the first 100 of 364 sites across 19 countries. Choose a country and city above to see the rest.
Plan to share: Yes — Anonymized individual patient level data will be provided in a secure access environment upon approval of a research proposal and a signed data sharing agreement.
Supporting information: Study protocol, Statistical analysis plan, Clinical study report
Time frame: Data are available 6 months after the primary publication or approval of the indication studied in the US and EU, whichever is later. Data will be indefinitely available for requesting.
Access criteria: A research proposal should be approved by an independent review panel and researchers should sign a data sharing agreement.
Data sharing details ↗ · vivli.org
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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Studies of the drug tested here: STX-478