A Study to Learn About the Study Medicine Called PF-07248144 in Combination with Fulvestrant in People with HR-positive, HER2-negative Advanced or Metastatic Breast Cancer who Progressed After a Prior Line of Treatment

About the Study

KATSIS-1 is a clinical trial exploring an investigational medicine called prifetrastat.

Over time, breast cancer cells can learn how to avoid standard hormone treatments and continue growing. Think of the cancer like a machine that has found a hidden workaround to keep running. Prifetrastat is designed to block that workaround and "rewire" the cells, making the cancer weak to standard hormone therapies once again.

 KATSIS-1 clinical trial participants will be randomly assigned, like a coin-flip, to one of two treatment groups. Throughout the trial, a dedicated medical team closely monitors their health and progress through regular clinic visits and scans.

What the Study Involves

• KATSIS-1 is a randomized, open-label Phase 3 clinical trial. Participants are randomly assigned to receive either the study treatment (prifetrastat) with fulvestrant or the study doctor’s choice of currently approved treatment (either exemestane or fulvestrant) plus another approved medicine called everolimus.

• Interested patients will complete screening tests to confirm eligibility, including medical history reviews, blood tests, physical exam, heart activity tests, and scans to measure tumors. 
• You will also be asked to participate in biomarker testing to confirm your eligibility.

To determine if you may be eligible for the KATSIS1 clinical trial, the study team will send your tumor sample for (biomarker) tests. These tests identify specific features of your breast cancer and help the study team understand how it may respond to the study treatment. The testing process, including shipping the tissue and carefully checking the results, usually takes about two to four weeks. Your tissue will only be tested if you give your permission. 

• Participants receive one of the two study treatments. Regular clinic visits are important for monitoring while you are on study treatment, including blood tests, scans to monitor tumor size and health assessments. Additional procedures, such as biopsies, may be needed.

Study participation also includes follow-up visits and brief assessments on how you are doing after you decide to stop study treatment. Additional commitment may be required, but the study team will discuss this further with you.  

Participants may receive reimbursement for treatment-related costs, such as travel. 

People may be eligible to join the KATSIS-1 study if they are 18 or older and have been diagnosed with HR-positive, HER2-negative advanced or metastatic breast cancer, which has spread elsewhere in the body after prior treatment with a CDK4/6 inhibitor or have received one additional systemic treatment before or after treatment with a CDK4/6 inhibitor.

Individuals may not be eligible if they have serious medical or psychiatric conditions, active infections, significant heart or brain disease, or abnormal kidney, liver, or blood test results. Exclusion may also apply to those with specific tumour gene alterations, extensive or rapidly progressing disease, no prior chemotherapy or targeted therapies for advanced disease, more than two prior systemic treatments, recent major surgery, or recent participation in another clinical trial.