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A Phase I/II Study of GVV858 Alone or in Drug Combination for Patients with Advanced Hormone Receptor‑Positive, HER2‑Negative Breast Cancer

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What is this trial about?

A plain-language summary of the goals, design and what participants do

Advanced hormone receptor positive, HER2-negative breast cancer and other advanced solid tumors are being studied. Hormone receptor positive means the cancer can grow when hormones are present, while HER2-negative means the tumor does not have extra HER2 protein. The study investigates the investigational drug GVV858, taken as a capsule by mouth, either by itself or together with standard hormone‑blocking treatments. These hormone therapies include the injectable medicine fulvestrant, the pill letrozole, and background hormone suppression with the injectable drugs leuprorelin acetate and goserelin. Hormone‑blocking treatments work by lowering hormone levels or blocking the hormones from reaching cancer cells.

The purpose of the study is to assess how safe the investigational drug is and to determine the appropriate dose when used alone or in combination with the hormone therapies.

Participants will first undergo screening tests, then begin taking the study medication in a series of visits. Depending on the study arm, they may receive an injection of the hormone blocker, a daily pill, or both, alongside the oral investigational drug. Throughout the study they will have regular check‑ups that include blood work, vital‑sign measurements, and heart rhythm checks to monitor safety. Treatment continues until the cancer shows growth, side effects become unacceptable, or the study ends.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline assessments

    After joining, initial medical examinations are performed to record current health status.

    Tests may include blood work, vital signs, electrocardiograms, and imaging studies to establish a reference point.

  2. Step 2

    Background hormone therapy

    The patient receives a subcutaneous injection of leuprorelin acetate or goserelin according to the study protocol.

    The exact dose, frequency and duration are defined by the trial schedule and are administered throughout the treatment period.

  3. Step 3

    Gvv858 single‑agent administration

    The patient takes oral capsules containing gvv858 as a single agent.

    The capsule is taken by mouth each day as instructed; the specific dose and length of treatment follow the protocol.

  4. Step 4

    Combination with fulvestrant (if assigned)

    For patients assigned to this arm, an intramuscular injection of fulvestrant is added to the regimen.

    The injection is given at intervals set by the study, continuing alongside daily gvv858 capsules.

  5. Step 5

    Combination with letrozole (if assigned)

    For patients assigned to this arm, oral letrozole is taken in addition to the daily gvv858 capsule.

    The tablet is taken each day; the schedule follows the trial protocol.

  6. Step 6

    Regular monitoring visits

    The patient attends scheduled clinic visits for safety monitoring, including laboratory tests, vital‑sign checks, and electrocardiograms.

    Imaging studies may be repeated to evaluate disease status according to the trial timetable.

  7. Step 7

    Treatment continuation or discontinuation

    Treatment is continued until disease progression, unacceptable side effects, or completion of the prescribed study period.

    If any dose reductions, interruptions, or discontinuations are required, they are managed according to protocol guidelines.

Who can join the trial?

8 criteria

  • You must be 18 years old or older.
  • You must have an advanced cancer for which the doctor believes no standard treatment is suitable.
  • If you have HR+/HER2- advanced breast cancer, the disease must have gotten worse while you were on, or you could not tolerate, at least one hormone‑based therapy combined with a CDK4/6 inhibitor, and you must have received at least one additional line of systemic treatment for the spread of cancer.
  • If you have a solid tumor (such as breast, ovarian, gastric, or esophageal cancer) that is locally advanced or has spread and shows CCNE‑1 amplification (a specific genetic change), you may be eligible.
  • For the Phase I expansion part, you may also have advanced ovarian, gastric, or esophageal cancer with CCNE‑1 amplification that has progressed after standard therapy.
  • If you have metastatic castration‑resistant prostate cancer, the disease must have progressed after at least one androgen receptor pathway inhibitor (a drug that blocks male hormones) and after a taxane‑based chemotherapy, and you must have had no more than three prior systemic treatments for the spread of cancer.
  • For Phase II, you must have HR+/HER2- advanced breast cancer that progressed after hormone therapy combined with a CDK4/6 inhibitor, and you must have had no more than two lines of hormone therapy for advanced disease and no prior chemotherapy or antibody‑drug conjugate therapy for advanced disease.
  • Your cancer must be measurable according to RECIST v1.1 (a system doctors use to measure tumor size). If you have breast cancer with no measurable tumor, you need at least one mainly bone lesion that can be accurately measured over time. If you have metastatic prostate cancer with no measurable disease by PCWG3 modified RECIST, you need at least one metastatic lesion visible on a bone scan before the first day of treatment.

Who cannot join the trial?

6 criteria

  • You cannot join if your bone marrow (the tissue that makes blood cells) or essential organ function (how well organs like the liver and kidneys work) is not adequate.
  • You cannot join if you have symptoms from cancer that has spread to the brain or spinal cord, called central nervous system (CNS) metastases, and you need special local treatment or higher doses of corticosteroids (steroid medicines) within two weeks before starting the study.
  • You cannot join if you have symptoms from cancer affecting major internal organs, known as visceral disease, especially a serious situation called a visceral crisis.
  • If you have breast cancer and are currently using hormone replacement therapy, or if you are a pre‑menopausal woman or a man with breast cancer and you are unwilling or unable to take a hormone‑lowering medicine called an LHRH agonist (examples: goserelin or leuprolide) for gonadal suppression, you cannot join.
  • Women who can become pregnant (women of childbearing potential) who are not willing to use highly reliable birth‑control methods cannot join.
  • If you are pregnant or nursing (breastfeeding), you cannot join.
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Investigated drugs

  • Leuprorelin acetate

    is a medication given as a subcutaneous injection that lowers estrogen levels by stopping the ovaries from making hormones. In this trial it is used as part of the standard background treatment for hormone‑sensitive breast cancer.

  • Goserelin

    is also injected under the skin and works in the same way as leuprorelin, suppressing the body’s production of estrogen. It is included in the trial as background endocrine therapy.

  • Fulvestrant

    is an injectable drug that is given into a muscle. It works by attaching to estrogen receptors on cancer cells and breaking them down, which helps stop the growth of tumors that need estrogen to grow. In this study it is combined with the investigational drug to see if the pair works better together.

  • Letrozole

    is an oral tablet that belongs to a class of medicines called aromatase inhibitors. It lowers estrogen levels by blocking the enzyme that makes estrogen from other hormones. The trial tests letrozole together with the new drug to see if the combination is safe and effective.

  • GVV858

    is an experimental oral capsule being studied for the first time in patients with advanced hormone‑receptor‑positive, HER2‑negative breast cancer and other solid tumors. The trial looks at how safe it is when taken alone and when combined with either fulvestrant or letrozole, and aims to find the best dose for future studies.

What is already known about the treatment

  • Leuprorelin acetate

    This drug is given as a subcutaneous injection. It is an approved medicine used to lower estrogen levels in hormone‑sensitive breast cancer and prostate cancer. It works by acting like a natural hormone that tells the pituitary gland to stop releasing signals that make the ovaries produce estrogen. It is classified as a gonadotropin‑releasing hormone (GnRH) agonist, a type of hormonal therapy.

  • Fulvestrant

    The medication is administered by intramuscular injection. It is an approved treatment for advanced hormone‑receptor‑positive, HER2‑negative breast cancer. It binds to the estrogen receptor on cancer cells and causes the receptor to be broken down, stopping estrogen from helping the tumor grow. It belongs to the class of estrogen‑receptor antagonists (selective estrogen receptor degraders).

  • GVV858

    GVV858 is taken as an oral capsule. It is currently an investigational drug being studied in clinical trials for advanced hormone‑receptor‑positive breast cancer and other solid tumors. The compound blocks estrogen signaling by attaching to the estrogen receptor and preventing it from working, which may slow tumor growth. It is classified as an experimental selective estrogen receptor degrader (SERD) and oral anticancer agent.

  • Goserelin

    This medication is delivered by subcutaneous injection. It is an approved hormone therapy for breast and prostate cancers that depend on hormones. It mimics a natural hormone that tells the brain to stop the signals that cause the ovaries to make estrogen, thereby reducing estrogen levels. It is a gonadotropin‑releasing hormone (GnRH) agonist, used as hormonal therapy.

  • Letrozole

    Letrozole is taken as an oral tablet. It is an approved aromatase inhibitor used to treat advanced hormone‑receptor‑positive breast cancer. It works by blocking the aromatase enzyme, which stops the body from converting other hormones into estrogen, lowering estrogen levels that fuel cancer growth. It belongs to the class of aromatase inhibitors, a form of hormonal therapy.

Investigated diseases

Advanced hormone receptor‑positive, HER2‑negative breast cancer - It is a type of breast cancer where the tumor cells have receptors for hormones such as estrogen or progesterone but lack excess HER2 protein. The disease usually begins as a localized tumor in the breast and can spread to nearby lymph nodes. Over time, cancer cells may grow and invade surrounding tissue. If not controlled, they can travel through the bloodstream to other parts of the body such as bone, liver, or lungs. The condition is considered advanced when it has spread beyond the breast or cannot be removed by surgery.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase I/IITrial ID2025-521911-38-00Protocol codeCGVV858A12101Estimated enrolment85 patientsSponsorNovartis Pharma AG

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