# Tersolisib

Source: https://onco.cc/drugs/tersolisib/  
OnCo record `tersolisib` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Tersolisib is an experimental small-molecule drug from Eli Lilly and in phase 3 trials for HR-positive / HER2-negative breast cancer, aimed at PIK3CA / PI3K-alpha.

## Summary

Tersolisib (STX-478, LY4064809) is a small-molecule drug developed by Eli Lilly and. Its target is PIK3CA / PI3K-alpha (the sponsor names mutant-selective PI3Kalpha (PIK3CA)). The sponsor states: Tersolisib (STX-478/LY4064809) is a mutant-selective PI3Kalpha inhibitor studied as monotherapy and in combination with fulvestrant, with or without CDK4/6-targeted endocrine therapy, in PIK3CA-mutated advanced solid tumours and HR-positive breast cancer. ClinicalTrials.gov describes the intervention as: STX-478 is a mutant-selective PI3Kα inhibitor. It is the investigational product in 2 recruiting or active industry-led phase 2 and phase 3 interventional cancer trials, including the phase 3 study NCT07174336 (A Study of Tersolisib (LY4064809/STX-478) With Other Anti-Cancer Treatments in Participants With Advanced Breast Cancer With a Genetic Change (PIK3CA)), in HR-positive / HER2-negative breast cancer. The largest, NCT05768139, plans to enrol 880 participants with primary completion expected 2030-07. Status reflects the highest phase registered on ClinicalTrials.gov; no efficacy results are recorded here.

## Fields

- Kind: Treatment
- Status: phase-3
- Last checked: 2026-09-11
- Tags: pipeline; ctgov-ingest
- Code: STX-478, LY4064809
- Modality: small molecule
- Mechanism: Tersolisib (STX-478/LY4064809) is a mutant-selective PI3Kalpha inhibitor studied as monotherapy and in combination with fulvestrant, with or without CDK4/6-targeted endocrine therapy, in PIK3CA-mutated advanced solid tumours and HR-positive breast cancer.

## Sources

- ClinicalTrials.gov: trials of Tersolisib: https://clinicaltrials.gov/search?intr=STX-478

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [HR-positive metastatic breast cancer after CDK4/6 inhibitors](https://onco.cc/cancers/hr-positive-metastatic-post-cdk46/)
- targets: [PIK3CA / PI3K-alpha](https://onco.cc/targets/pik3ca/)
- companies: [Eli Lilly (incl. Loxo)](https://onco.cc/companies/eli-lilly/)
- trials: [A Study of Tersolisib (LY4064809/STX-478) With Other Anti-Cancer Treatments in Participants With Advanced Breast Cancer With a Genetic Change (PIK3CA)](https://onco.cc/trials/pik3ca-2/)

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