An observational study in Breast Cancer, sponsored by AstraZeneca. Recruiting at 14 sites in 2 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-14.
Sponsored by AstraZeneca · Observational
A longitudinal, non-interventional study with trastuzumab deruxtecan for patients with HER2-low expressing unresectable or metastatic breast cancer in Bulgaria and Slovenia
EXPLORE Non-Interventional Study for HER2-low Breast Cancer Treatment with T-DXd
Background:
HER2 is a prognostic marker in various cancers, including breast cancer (BC). Traditionally categorized as HER2-positive or HER2-negative, recent advancements with anti-HER2 ADCs, like trastuzumab deruxtecan (T-DXd), have shown benefits for HER2-low status BC. The DB-04 trial demonstrated significant survival benefits with T-DXd, leading to its EMA approval for HER2-low BC in January 2023.
Study Rationale:
Limited real-world evidence exists for T-DXd in HER2-low BC, particularly in the Balkans. The EXPLORE study aims to fill this gap by collecting real-world data in Bulgaria and Slovenia.
Objectives:
Primary Objective:
Describe real-world Time to Next Treatment (rwTTNT1) of T-DXd in HER2-low unresectable or metastatic BC (mBC).
Secondary Objectives:
Describe pre-T-DXd treatment patterns at baseline. Describe patient demographics and clinical characteristics at baseline. Describe rwTTNT1 by prior therapy lines in the metastatic setting and by hormone receptor (HR) status.
Evaluate real-world Time to Treatment Discontinuation (rwTTD1).
Exploratory Objectives:
Evaluate real-world progression-free survival (rwPFS1). Characterize subsequent treatments and post-progression endpoints (rwTTNT2, rwTTD2, rwPFS2).
Describe biopsy patterns. Evaluate reasons for discontinuation (rwTTNT1 and rwTTNT2). Describe T-DXd treatment changes over time. No formal hypothesis is set.
Methods:
Study Design:
Observational, longitudinal, non-interventional study in Bulgaria and Slovenia. Patients with unresectable or mBC starting T-DXd within 30 days of enrolment. Data from hospital charts at routine visits.
Population:
Adults (≥18 years) with HER2-low mBC, initiating T-DXd independent of the study.
Exposure:
T-DXd treatment details (dose, duration) and other therapies recorded. Recommended T-DXd dose: 5.4 mg/kg IV every 3 weeks.
Outcomes:
Primary: Time from T-DXd initiation to subsequent therapy or death. Exploratory: Various survival measures, biopsy patterns, reasons for discontinuation, and treatment changes.
Sample Size:
Approximately 135 patients (100 in Bulgaria, 35 in Slovenia).
Statistical Analysis:
Descriptive analyses for cohort characteristics. Kaplan-Meier method for time-to-event endpoints. Subgroup analyses by prior therapy lines and HR status.
Data Collection:
Data from paper or electronic health records. Single anonymized dataset via electronic case report forms (CRFs).
14,825 studies on the registry are indexed under Breast Neoplasms; 3,319 are open to participants now.
This study's planned enrollment of 138 is below the median of 184 across 3,235 observational studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →AstraZeneca is the lead sponsor of 3,499 studies on the registry; 270 are open to participants now.
Of its 368 completed or terminated interventional studies of FDA-regulated products, 178 (48%) have results posted.
Counted across the registry records on this site, refreshed daily.
Study Population:
Criteria:
Age: Adult patients (≥18 years). Diagnosis: Confirmed diagnosis of unresectable or metastatic breast cancer (mBC).
HER2 Status: Documented HER2-low status. Treatment Decision: Patients for whom the decision to initiate trastuzumab deruxtecan (T-DXd) treatment has been made independently and prior to enrolment in the study.
Enrollment:
Timing: Patients must be enrolled within 30 days before the administration of the first T-DXd infusion.
Consent: Patients must provide written informed consent for data collection.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
HER2
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Metastases
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Adjuvant and neoadjuvant
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
T-DXd
Real-world Time to Next Treatment (rwTTNT1, median, 95% CI, measured in months)
The duration from initiation of trastuzumab deruxtecan (T-DXd) treatment to the start of the subsequent therapy or death from any cause, whichever occurs first, assessed up to 19 months.
Time frame: Baseline up to 19 months
Describe type and proportion of previous treatments for unresectable or mBC and comorbidities
Prior treatments: surgery, chemotherapy, radiotherapy, therapies in neoadjuvant/adjuvant/advanced setting; treatment line (special focus should be given on endocrine and chemotherapy recycling in the metastatic setting). The timeline for these treatments will include all therapies administered from the time of breast cancer diagnosis.
Time frame: Baseline
Duration of previous treatments and number of treatment lines
Start and stop date, if available
Time frame: Baseline
Response to previous treatments
To describe patients' response to previous treatment, as applicable: clinical response (partial response/complete response/stable disease/disease progression; if progression: date and site of progression)
Time frame: Baseline
Mean (SD) age at diagnosis
Describe the patients' mean (SD) age at diagnosis
Time frame: Baseline
Mean (SD) age at T-DXd start
To describe patients' mean (SD) age at T-DXd start
Time frame: Baseline
Proportion of males and females
To describe the proportion of males and females
Time frame: Baseline
Proportion of patients with HR+ vs HR- tumors
Describe the proportion of patients with HR+ vs HR- tumors
Time frame: Baseline
Distribution by smoking status
Describe the patients' smoking status. Includes electronic cigarettes/vapes
Time frame: Baseline
Type and proportion of comorbidities
Comorbidities (including cardiovascular diseases, pulmonary disorders, hepatic disorders, renal disorders, blood and lymphatic system disorders, metabolism and nutrition disorders, gastrointestinal disorders, hepatobiliary disorders, central nervous system \[CNS\] disorders, eye disorders, skin disorders and musculoskeletal and connective tissue disorders, infections and infestations and other relevant
Time frame: Baseline
Distribution by ECOG status
Describe patients' ECOG PS at index date
Time frame: Baseline
mean (SD) duration of disease (at index), measured in months or years
Describe patients' mean duration of disease through date of initial diagnosis and date of diagnosis of unresectable or metastatic breast cancer, as applicable
Time frame: Baseline
HER2-low status and type and proportion of metastatic sites
Describe patients' HER2-low status and type and proportion of metastatic sites through most recent HER2-low status, new metastatic sites since the time of mBC diagnosis, disease burden (all disease sites, including the presence/absence of brain metastases \[stable/active\]
Time frame: Baseline
rwTTNT1 by Number of Prior of Therapy Lines for Metastatic Disease (median, 95% CI, measured in months, 1 vs 2 vs 3+ Lines)
Describe rwTTNT1 stratified by the number of prior therapy lines in the metastatic setting.
Time frame: Baseline up to 19 months
rwTTNT1 by HR-status (median, 95% CI, measured in months, HR+ vs HR-)
Describe rwTTNT1 stratified by hormone receptor (HR) status.
Time frame: Baseline up to 19 months
Real-world Time to Treatment Discontinuation (rwTTD1, median, 95% CI, measured in months)
Evaluate the duration from the start of T-DXd treatment until its discontinuation or death, whichever occurs first.
Time frame: Baseline up to 19 months
Real-world Progression-Free Survival (rwPFS1, median, 95% CI, measured in months)
Evaluate the duration from the start of T-DXd treatment until disease progression or death, whichever occurs first.
Time frame: Baseline up to 19 months
Real-world Time to Second Next Treatment (rwTTNT2, median, 95% CI, in months)
Time frame: Baseline up to 19 months
Real-world Time to Subsequent Treatment Discontinuation (rwTTD2, median, 95% CI, measured in months)
Time frame: Baseline up to 19 months
Real-world progression free survival 2 (rwPFS2, median, 95% CI, measured in months)
Time frame: Baseline up to 19 months
Biopsy Patterns (number of biopsies conducted prior to the start of T-DXd treatment)
Describe the number of biopsies conducted prior to the start of T-DXd treatment.
Time frame: Baseline, assessed for the past 10 years
Biopsy Patterns (the time from the last fresh biopsy to the start of T-DXd treatment, measured in months or years)
Describe the time from the last fresh biopsy to the start of T-DXd treatment.
Time frame: Baseline, assessed for the past 10 years
Reasons for Discontinuation (rwTTNT1 and rwTTNT2)
Evaluate the reasons for discontinuation of T-DXd treatment and subsequent therapy due to disease progression, adverse events, or other reasons.
Time frame: Baseline up to 19 months
T-DXd Treatment Changes Over Time
Proportion of patients with dose changes, proportion of patients with dose reductions, interruption(s), or treatment discontinuation
Time frame: Baseline up to 19 months
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Plan to share: Yes — Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal Vivli.org. All requests will be evaluated as per the AZ disclosure commitment: https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure
Time frame: AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA PhRMA Data Sharing Principles. For details of our timelines, please rerefer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.
Access criteria: When a request has been approved AstraZeneca will provide access to the anonymized individual patient-level data via secure research environment Vivli.org. Signed Data Usage Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information.
Data sharing details ↗ · vivli.org
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