Sponsor: Seagen, a wholly owned subsidiary of Pfizer (industry)
Phase: 2
Start date: May 20, 2024
Planned enrollment: 172
Disitamab vedotin (RC48, Aidixi) is an antibody-drug conjugate (ADC) that targets HER2-expressing cancers. It consists of a humanized anti-HER2 monoclonal antibody (disitamab) conjugated to the cytotoxic agent monomethyl auristatin E (MMAE) via a cleavable vedotin linker [1]. The drug works through multiple mechanisms including direct cytotoxicity to HER2-expressing cells, bystander effect on neighboring cells, immunogenic cell death, and inhibition of HER2 signaling pathways. It received its first approval in China in June 2021 for HER2-overexpressing locally advanced or metastatic gastric cancer after at least two lines of chemotherapy [2].
Clinical trials have shown promising results across multiple cancer types. In HER2-expressing metastatic breast cancer, the drug demonstrated objective response rates of 42.9% in HER2-overexpressing and 33.3% in HER2-low disease, with median progression-free survival of 5.7 and 5.1 months respectively [3]. In urothelial carcinoma, when combined with the immunotherapy drug toripalimab, it showed a 73.2% response rate with median progression-free survival of 9.2 months [4]. Common adverse events include elevated liver enzymes, peripheral neuropathy, asthenia, and neutropenia. Grade 3 or higher adverse events occurred in about 40-44% of patients across trials, but were generally manageable.
The drug is currently being investigated in multiple ongoing clinical trials, including phase 3 studies in various cancers. It is being studied both as monotherapy and in combination with other agents like immunotherapy drugs and targeted therapies. Development is focused on both HER2-overexpressing and HER2-low expressing cancers, with studies ongoing in breast cancer, gastric cancer, urothelial cancer, and other solid tumors.
[1] AACR Abstract on Mechanism of Action [2] Review Article on Development and Approval [3] Phase I/Ib Study in Breast Cancer [4] Phase 1b/2 Study in Urothelial Cancer
Last updated: Dec 2024
Goal: The trial aims to assess the safety, tolerability, and preliminary efficacy of disitamab vedotin in combination with tucatinib in patients with locally advanced or metastatic HER2-expressing breast cancer or gastric/gastroesophageal junction adenocarcinoma. The study will determine optimal dosing and evaluate the benefit/risk profile of this combination across HER2-low and HER2-positive disease settings.
Patients: Eligible patients have locally advanced or metastatic breast cancer or gastric/gastroesophageal junction adenocarcinoma with measurable disease and HER2 expression (either HER2-low or HER2-positive), ECOG 0-1, and must have received and progressed on or been intolerant to standard therapies. Four main cohorts will be studied based on cancer type (breast or gastric/GEJC) and HER2 status (low or positive).
Design: The trial uses an open-label, randomized, multi-phase design. Initial dose escalation and optimization phases inform combination tolerability and identify appropriate dosing, followed by a dose expansion phase with four specific HER2-low and HER2+ patient cohorts. Approximately 172 patients will be enrolled.
Treatments: All patients receive the combination of disitamab vedotin and tucatinib. Disitamab vedotin is an antibody-drug conjugate targeting HER2, composed of a humanized anti-HER2 monoclonal antibody linked to the cytotoxic agent MMAE. In clinical trials, it has demonstrated promising ORR and PFS in both HER2-high and HER2-low metastatic breast cancer and is approved in China for metastatic gastric cancer after chemotherapy. Common adverse events include elevated liver enzymes, neuropathy, asthenia, and neutropenia, with grade 3+ AEs manageable in most patients. Tucatinib is an approved small molecule HER2 tyrosine kinase inhibitor marketed as TUKYSA and is included in the regimen for its efficacy in HER2-positive disease.
Outcomes: Primary endpoints include safety measures (rates of laboratory abnormalities, dose-limiting toxicities, adverse events, and dose modifications) and efficacy (objective response rate per RECIST v1.1). Secondary endpoints include duration of response, disease control rate, progression-free survival, overall survival, pharmacokinetics, and immunogenicity (ADA incidence).
Burden on patient: The patient burden is moderate to high, particularly in the dose escalation phase. Participants will undergo frequent clinic visits for safety assessments, adverse event monitoring, laboratory testing, pharmacokinetic blood draws, and imaging for disease assessment. Additional tumor biopsies may be required for HER2 status confirmation, and patients with gastric/GEJ cancer must provide archival or repeat tumor tissue. Such intensive monitoring and testing exceed standard of care and are typical for early phase combination studies.
Inclusion Criteria:
General Inclusion Criteria
* Measurable disease according to RECIST v1.1
* Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1
Dose Escalation and Optimization Phase Inclusion Criteria
* Histologically or cytologically confirmed diagnosis of gastric or gastroesophageal junction adenocarcinoma or breast carcinoma
* Locally-advanced, unresectable, or metastatic stage
* Must have experienced disease progression on or after standard of care therapies or be intolerant of standard of care therapies.
Cohort A (HER2-Low Breast Cancer) Inclusion Criteria
* Histologically or cytologically confirmed diagnosis of breast carcinoma
* Locally-advanced, unresectable, or metastatic stage
* HER2-low status determined by most recent local assessment (IHC 1+ or IHC 2+/ISH-negative)
* Prior therapies requirements
* No more than 3 prior systemic cytotoxic chemotherapy regimens (including ADCs) for LA/mBC.
* Participants with known BRCA mutation must have received a PARP-inhibitor where available and not medically contraindicated
* Have progression on or after, or intolerant to, T-DXd, sacituzumab govitecan, or other topoisomerase I inhibitor therapies, if available as local standard of care therapy
* Participants with HR+ tumors must have intolerance to endocrine therapy or endocrine therapy refractory disease:
* Progressed on ≥2 lines of endocrine therapy for LA/mBC AND had received a CDK4/6 inhibitor in the adjuvant or metastatic setting OR
* Progressed on 1 line of endocrine therapy for LA/mBC AND had a relapse while on adjuvant endocrine therapy after definitive surgery for primary tumor AND had received a CDK4/6 inhibitor in the adjuvant or advanced setting
* Participants with HR negative, HER2-low and PD-L1-positive (CPS 10 or greater) tumors must have received pembrolizumab with chemotherapy if available as local standard of care therapy.
* Participants with HR negative, HER2-low and PD-L1-positive (CPS 10 or greater) tumors must have received pembrolizumab (or other PD-(L)1 inhibitor) with chemotherapy if available as local standard of care therapy and not medically contraindicated.
Cohort B (HER2+ Breast Cancer) Inclusion Criteria
* Histologically or cytologically confirmed diagnosis breast carcinoma
* Locally-advanced, unresectable, or metastatic stage
* HER2+ status determined by most recent local assessment (IHC 3+ or IHC 2+/ISH+)
* Participants must have:
* Received prior trastuzumab, pertuzumab and a taxane if available as local standard of care therapy for advanced disease.
* Have progression on or after, or intolerant to, T-DXd or other topoisomerase I inhibitor therapies
* No more than 3 prior systemic cytotoxic chemotherapy regimens (including ADCs) for LA/mBC
Cohort C (HER2-Low Gastric or Gastroesophageal Junction Adenocarcinoma) Inclusion Criteria
* Histologically or cytologically confirmed diagnosis of gastric or gastroesophageal junction adenocarcinoma
* Locally-advanced, unresectable, or metastatic stage
* HER2-low expression defined as IHC 1+ or IHC 2+/ISH-negative determined by most recent local assessment
* Willing and able to provide archival or newly obtained formalin-fixed paraffin-embedded (FFPE) tumor tissue blocks
* Participants must have received:
* Prior systemic therapy with platinum, fluorouracil, or taxane for locally advanced unresectable or metastatic disease
* Progression within 6 months of last dose of (neo)adjuvant cytotoxic chemotherapy is considered as 1 line of systemic therapy for LA/mGC/GEJC
* Prior anti-PD-(L)1 therapy is allowed
* No more than 2 prior systemic cytotoxic chemotherapy regimens (including ADC) for LA/mGC/GEJC
* Must not have received prior treatment with HER2 directed therapy
Cohort D (HER2+ LA/mGC/GEJC) Inclusion Criteria
* Histologically or cytologically confirmed diagnosis of gastric or gastroesophageal junction adenocarcinoma
* Locally-advanced, unresectable, or metastatic stage
* HER2+ status determined by most recent local assessment (IHC 3+ or IHC 2+/ISH+)
* Participants must have:
* Received prior trastuzumab plus fluoropyrimidine and platinum containing chemotherapy if no contraindication.
* Prior T-DXd treatment is allowed
* Prior PD1 inhibitor therapy is allowed
* No more than 2 prior systemic cytotoxic chemotherapy regimens (including ADCs) for LA/mGC/GEJC
Exclusion Criteria:
* Known hypersensitivity to any excipient contained in the drug formulation of disitamab vedotin or tucatinib
* Prior therapy with ADCs with MMAE payload
* Prior therapy with tucatinib
* Active CNS and/or leptomeningeal metastasis.
* Participants who have received prior systemic anticancer treatment including investigational agents within 4 weeks prior to first dose of study treatment
* History of other invasive malignancy within 3 years before the first dose of study intervention, or any evidence of residual disease from a previously diagnosed malignancy.
* Unable to swallow oral tablets or capsules or any significant GI disease which would preclude the adequate oral absorption of medications
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