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ABCSG 65 / DEFINTIVE Study Details


Diagnostic HER2DX-guided treatment For patIeNts wIth early-stage HER2-posiTIVE breast cancer

An international, multicenter, prospective, two-arm, randomized, open-label Phase III study designed to demonstrate that personalized treatment decisions in HER2-positive early-stage breast cancer using the HER2DX® diagnostic test improve quality of life without compromising outcomes and survival rates.

Study Start: (global): 11/2024,  FPI 11/2024
(national): 07/2025
Coordinating Investigator AT: Rupert Bartsch, Vienna
Participants: 315 (global), 70 (national)
Study Design:
(Click to enlarge)		 Study Design:

Treatment

Patients who meet randomization eligibility criteria will be randomized in a 1:1 ratio:

  • Arm A: Blinded HER2DX result – Treatment according to the physician’s choice and local guidelines
  • Arm B: Available HER2DX result – HER2DX guided treatment

HER2DX test results will be shown only for patients randomized to ARM B.

Randomization will be stratified by the following factors:

  • HER2DX risk group (high vs. low groups): Risk of recurrence following curative intent therapy.
  • HER2DX pCR likelihood group (high vs. medium vs. low groups): The likelihood of the tumor completely disappearing after undergoing neoadjuvant trastuzumab-based CT.

Primary Objectives

  • To determine whether there is an improvement in the health-related quality of life (HRQoL) following tailored treatment by HER2DX compared with standard of care treatment.
  • To evaluate whether the strategy of tailoring treatment by HER2DX presents a similar rate of responses than the standard of care treatment.

Secondary Objectives

  • To evaluate other HRQoL patient-reported outcomes (functional and symptom values) following tailored treatment by HER2DX compared with standard of care treatment.
  • To evaluate whether strategy of tailoring treatment by HER2DX presents similar effectiveness outcomes than the standard of care treatment.
  • To evaluate the association between HER2DX scores and efficacy outcomes
  • To assess the safety and tolerability of test guided treatment and their corresponding standard treatment.
  • To evaluate patient experience in control arm compared to those treated using the test and assess whether the inclusion of HER2DX test has an impact on patient experience.
  • To analyze the economic impact of the HER2DX test.
  • To evaluate whether the potential treatment de-escalation following tailored treatment by HER2DX could have impact in the work productivity.

Exploratory Objective

  • To explore biomarkers identified at baseline using available clinical or pathological data, or remaining RNA from tumor samples.

Patient Population

  • The target population of interest in this study consists of patients with HER2- early breast cancer stage II-IIIa.
  • This trial will be conducted in men and pre/postmenopausal women.
  • Patients have not received any prior treatment for breast disease.
  • Patients enrolled in this protocol are permitted to participate in additional parallel investigational drug(s) and/or device(s) studies while on treatment as long as it does not interfere with the treatment, tests and follow-up of the DEFINITIVE protocol.

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