Impact of Genetic Variants on the Toxicity of Antibody-Drug Conjugates in Locally Advanced or Metastatic Breast Cancer: The Role of the UGT1A1 Gene as a Predictive Biomarker of Therapeutic Response

May 6, 2026 updated by: Isabel Blancas López Barajas, Fundación Pública Andaluza para la Investigación Biomédica Andalucía Oriental

The metabolism of anticancer drugs is influenced by genetic variants that affect their bioavailability and toxicity. In the case of antibody-drug conjugates (ADCs), such as sacituzumab-govitecan (SG), trastuzumab-deruxtecan (T-DXd), and datopotamab-deruxtecan (Dato-DXd), the enzyme UDP-glucuronosyltransferase 1A1 (UGT1A1) plays a central role in the glucuronidation and elimination of their cytotoxic components. In particular, the metabolism of SN-38, the active metabolite of irinotecan and SG, is highly influenced by variants in UGT1A1, leading to drug accumulation and the development of severe toxicities. Patients with variants such as UGT1A1*28 (rs3064744) and UGT1A1*6 (rs4148323) exhibit reduced enzyme activity, increasing the risk of neutropenia and severe diarrhea.

The relevance of UGT1A1 is not limited to sacituzumab-govitecan; its role in the elimination of camptothecin derivatives suggests it could also impact the toxicity of trastuzumab-deruxtecan and datopotamab-deruxtecan, which contain deruxtecan, a cytotoxic agent 10 times more potent than irinotecan. Despite strong evidence linking the UGT1A1 genotype to irinotecan toxicity, there are currently no established pharmacogenetic recommendations for antidiuretic peptides (ADCs) in metastatic breast cancer.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Study Type

Observational

Enrollment (Estimated)

70

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • Spain
    • Granada
      • Granada, Granada, Spain, 18016
        • Recruiting
        • Hospital Universitario Clinico San Cecilio
        • Contact:
        • Principal Investigator:
          • Isabel Blancas López-Barajas, MD, PhD

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

Study Population

Patients with early, locally advanced, or metastatic breast cancer treated with antibody-drug conjugates in a real-world clinical setting at a single tertiary hospital.

Description

Inclusion Criteria:

  • Patients aged 18 years or older.
  • Patients diagnosed with breast cancer starting or undergoing treatment with Sacituzumab Govitecan, Trastuzumab Deruxtecan, or Datopotamab Deruxtecan.
  • Provision of signed informed consent for the genetic study.

Exclusion Criteria:

  • Patients who are ultimately not treated with the specified Antibody-Drug Conjugates.
  • Refusal to provide informed consent for genetic analysis.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
Patients undergoing treatment with sacituzumab govitecan
Standard clinical dose of sacituzumab govitecan administered as per routine clinical practice.
Drug: Sacituzumab Govitecan
Administered according to standard clinical practice and product label.
Patients undergoing treatment with trastuzumab-deruxtecan
Standard clinical dose of trastuzumab-deruxtecan administered as per routine clinical practice.
Drug: Trastuzumab deruxtecan
Administered according to standard clinical practice and product label.
Patients undergoing treatment with datopotamab deruxtecan
Standard clinical dose of datopotamab deruxtecan administered as per routine clinical practice.
Drug: Datopotamab Deruxtecan
Administered according to standard clinical practice and product label.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Incidence of Severe Drug-Related Toxicities (Grade ≥ 3)
Time Frame: From the start of treatment until the end of the follow-up period (up to 2 years).
Number of patients experiencing severe hematological or gastrointestinal toxicities (defined as Grade 3 or higher according to CTCAE v5.0) that are definitely, probably, or possibly related to the treatment with Sacituzumab Govitecan, Trastuzumab Deruxtecan, or Datopotamab Deruxtecan.
From the start of treatment until the end of the follow-up period (up to 2 years).

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Frequency of UGT1A1*28 Allele
Time Frame: At baseline (once the genetic study is performed).
Distribution and allelic frequency of the UGT1A1*28 variant in the study population of breast cancer patients.
At baseline (once the genetic study is performed).
Correlation Between Genetic Variants and Toxicity Severity
Time Frame: Analyzed at the completion of the 2-year study period.
Statistical association (using Odds Ratio) between the identified genetic variants (rs4148323, rs35350906, rs3064744, rs887829, rs111741722) and the severity of adverse events.
Analyzed at the completion of the 2-year study period.
Predictive Model for Severe Toxicity
Time Frame: At the end of the study (2 years).
Design of a predictive model based on genetic markers to anticipate the appearance of severe toxicities for each ADC studied.
At the end of the study (2 years).

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Fundación Pública Andaluza para la Investigación Biomédica Andalucía Oriental

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

July 15, 2025

Primary Completion (Estimated)

December 31, 2026

Study Completion (Estimated)

March 31, 2027

Study Registration Dates

First Submitted

May 6, 2026

First Submitted That Met QC Criteria

May 6, 2026

First Posted (Actual)

May 13, 2026

Study Record Updates

Last Update Posted (Actual)

May 13, 2026

Last Update Submitted That Met QC Criteria

May 6, 2026

Last Verified

May 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • FIB-MAM-2025-04

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

Individual participant data will not be shared to ensure patient confidentiality and compliance with data protection regulations. Aggregate results will be available through scientific publications.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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