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Testing STX-478 for advanced solid tumors and breast cancer

First-in-Human Study of STX-478, a Mutant-Selective PI3Kα Inhibitor as Monotherapy and in Combination With Other Antineoplastic Agents in Participants With Advanced Solid Tumors

Phase1; Phase2 Interventional Eli Lilly and Company · NCT05768139

This study is testing a new cancer drug called STX-478 to see if it can help people with advanced solid tumors and breast cancer, both on its own and when used with other treatments.

Quick facts

PhasePhase1; Phase2
Study typeInterventional
Enrollment880 (estimated)
Ages18 Years and up
SexAll
SponsorEli Lilly and Company Industry-sponsored
Locations66 sites (Los Angeles, California and 65 other locations)
Trial IDNCT05768139 on ClinicalTrials.gov

What this trial studies

This study evaluates the safety and effectiveness of STX-478, both alone and in combination with other cancer treatments, in patients with advanced solid tumors, particularly those with specific genetic mutations. It consists of three parts: the first part assesses STX-478 as a standalone treatment, the second part examines its use alongside fulvestrant for hormone receptor-positive breast cancer, and the third part explores its combination with endocrine therapies and CDK4/6 inhibitors. Each participant will undergo a screening period followed by treatment over a defined timeframe.

Who should consider this trial

Good fit: Ideal candidates are adults aged 18 and older with advanced or refractory solid tumors that harbor PI3Kα mutations.

Not a fit: Patients with uncontrolled diabetes, symptomatic brain or spinal metastases, or those with distinct malignancies within the last two years may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could provide a new treatment option for patients with advanced solid tumors and hormone receptor-positive breast cancer.

How similar studies have performed: Other studies have shown promise with similar approaches targeting PI3Kα mutations, indicating potential for success.

Eligibility criteria

Show full inclusion / exclusion criteria 
Key Inclusion Criteria:

* Has an advanced or refractory solid tumor malignancy that is metastatic or locally advanced and unresectable (as specified by Cohort)
* Has a new or recent tumor biopsy (collected at screening, if feasible) or will provide an adequate tissue sample prior to screening
* Has a tumor that harbors a documented PI3Kα mutation (cohort specific criterion for cohort-specific mutation types)
* Is ≥18 years of age at the time of signing the ICF
* Has an ECOG performance status score of 0 or 1 at screening
* Has adequate organ function as defined per protocol

Key Exclusion Criteria:

* Has history (within ≤2 years before screening) of a solid tumor or hematological malignancy that is histologically distinct from the cancers being studied
* Has symptomatic brain or spinal metastases
* Has an established diagnosis of uncontrolled diabetes mellitus (defined as HbA1c ≥8% and/or FBG ≥140 mg/dL \[7.7 mmol/L\] and/or requiring or required insulin).
* Has had prior treatment with PI3K/AKT/mTOR inhibitor(s), except in certain circumstances
* Has had treatment with any local or systemic antineoplastic therapy or investigational anticancer agent within 14 days or 4 half-lives, whichever is longer, prior to the initiation of study treatment up to a maximum washout period of 28 days. Endocrine therapy does not require a washout period if the patient is enrolling in a cohort with the same combination endocrine therapy.
* Has toxicities from previous anticancer therapies that have not resolved to baseline levels or CTCAE grade ≤1, with the exception of alopecia and peripheral neuropathy.
* Has had radiotherapy within 14 days before the initiation of study treatment

Where this trial is running

Los Angeles, California and 65 other locations

+16 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Breast CancerSolid Tumors, AdultBreast NeoplasmsNeoplasms by SiteNeoplasmsBreast DiseasesHER2-negative breast cancerHR-positive breast cancer
Last reviewed 2026-06-09 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.