Observational Study of Gut Microbiota in Abemaciclib-Treated Patients With and Without Diarrhea

Gut Microbiota Changes in Breast Cancer Patients Treated With Abemaciclib and Correlation With Drug-Induced Diarrhea: An Observational Cohort Study

Why is this study being done? Many patients with a type of breast cancer (called HR-positive) take a medicine called Abemaciclib. While this medicine is effective, a very common side effect is diarrhea, which can be severe enough to disrupt treatment and reduce quality of life. The reason why some patients get diarrhea and others do not is not well understood. This study aims to investigate whether the natural bacteria living in the gut (known as the gut microbiome) play a role in this side effect. Researchers will compare the gut bacteria of patients who develop diarrhea with those who do not.

What will happen in the study? This is an observational study, which means that patients will receive their normal cancer treatment and will not be given any new or experimental drugs as part of this initial phase.

• Patients who are already being treated with Abemaciclib will be invited to join.
• They will be placed into one of two groups: those who experience diarrhea and those who do not.
• Participants will be asked to provide stool (feces) samples and may also provide optional blood samples at specific times during their treatment.
• Researchers will analyze these samples in the lab to study the types and functions of the gut bacteria.

Who can participate?

• Adult women (aged 18-75) diagnosed with HR-positive breast cancer.
• Currently receiving treatment with Abemaciclib for at least 2 weeks.
• Must be willing to provide informed consent and follow the study procedures.

What are the potential benefits? Participants will not receive any direct medical benefit from taking part in this study. However, the information learned may help researchers better understand why diarrhea occurs and, in the future, could lead to new ways to prevent or treat this side effect for other cancer patients.

How is privacy protected? All personal information and samples collected will be de-identified using a unique code. This means that the data used for analysis cannot be directly linked back to the participant's identity. All data is stored securely according to strict ethical guidelines.

Study Overview

• Status: Recruiting
• Conditions: Breast Neoplasms; Microbiome; Hormone Receptor-Positive Breast Cancer; Abemaciclib; Abemaciclib-related Diarrhea; Drug-induced Diarrhea; Gastrointestinal Microbiome (Focus)

• Study Type: Observational
• Enrollment (Estimated): 60

Contacts and Locations

• Study Contact: Name: Xinhong Wu Principal Investigator; Phone Number: 18602726300; Email: wuxinhong_9@sina.com

Study Locations

• China
  • Hubei
    • Wuhan, Hubei, China, 430079
      • Recruiting
      • Hubei Cancer Hospital
      • Contact: Xinhong Wu; Phone Number: 18602726300; Email: wuxinhong_9@sina.com
      • Contact: Wu; Email: wuxinhong_9@sina.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

This study will enroll a prospective cohort of female patients with hormone receptor-positive (HR⁺) breast cancer who are receiving treatment with Abemaciclib (as monotherapy or in combination) as part of their standard clinical care at Hubei Cancer Hospital. Participants will be prospectively assigned into two groups based on the presence or absence of drug-induced diarrhea, as defined by CTCAE v5.0 criteria: the Diarrhea Group and the Non-Diarrhea (Control) Group. The study involves the collection of clinical data, fecal samples, and optional blood samples for microbiome and biomarker analysis. No investigational intervention is administered in this phase of the study.

Description

Inclusion Criteria:

1. Aged 18 to 75 years.
2. Diagnosed with hormone receptor-positive (HR⁺) breast cancer.
3. Currently receiving treatment with Abemaciclib (either as monotherapy or in combination with endocrine therapy) for a duration of at least 2 weeks.
4. Willing and able to provide written informed consent for participation in the study.

Exclusion Criteria:

1. History of major gastrointestinal diseases, such as inflammatory bowel disease, Crohn's disease, ulcerative colitis, or intestinal obstruction, or having undergone major gastrointestinal surgery.
2. Recent use (within 1 month) of antibiotics, probiotics, or traditional Chinese medicine that may alter gut function.
3. Pregnant or lactating women.
4. Unwilling to provide informed consent or considered by the investigator to be unsuitable for the study for any other reason.

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort
Abema-Diarrhea; HR-positive breast cancer patients who develop diarrhea (Grade 1 or higher as per CTCAE v5.0 criteria) during treatment with Abemaciclib. This group will not receive any investigational intervention as part of the observational study. Fecal and blood samples will be collected for microbiome and biomarker analysis.
Abema-NoDiarrhea; HR-positive breast cancer patients who do not develop diarrhea (Grade 0 as per CTCAE v5.0 criteria) during treatment with Abemaciclib. This group serves as the control cohort and will not receive any investigational intervention as part of the observational study. Fecal and blood samples will be collected for microbiome and biomarker analysis.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Difference in gut microbiota beta diversity	Beta diversity of the gut microbiome (e.g., Weighted UniFrac distance) will be compared between the diarrhea group and the non-diarrhea group to assess overall microbial community structure differences.	Through study completion, an average of 6 months.
Identification of specific bacterial species enriched in non-diarrhea group	Metagenomic sequencing data will be analyzed (e.g., using LEfSe) to identify bacterial species that are significantly enriched in the non-diarrhea group compared to the diarrhea group (LDA Score > 2, p-value < 0.05).	Through study completion, an average of 6 months.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Difference in gut microbiota alpha diversity	Alpha diversity indices (Shannon, Chao1) of the gut microbiome will be compared between the diarrhea group and the non-diarrhea group.	Through study completion, an average of 6 months.
Difference in metagenomic functional pathways	Differential abundance analysis of functional pathways (e.g., KEGG Level 2/3) derived from metagenomic sequencing data between the two groups.	Through study completion, an average of 6 months.
Differential metabolites in serum	Differences in serum metabolomic profiles between the diarrhea and non-diarrhea groups.	Through study completion, an average of 6 months.
Difference in systemic inflammatory cytokine levels	Levels of inflammatory cytokines (e.g., IL-6, TNF-α, CRP) in serum will be compared between the two groups.	Through study completion, an average of 6 months.

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Predictive potential of baseline gut microbiota	Exploratory analysis to assess the potential of baseline gut microbiota features for predicting the risk of developing Abemaciclib-induced diarrhea.	Through study completion, an average of 6 months.

Collaborators and Investigators

• Sponsor: Hubei Cancer Hospital

Study record dates

Study Major Dates

• Study Start (Actual): December 21, 2025
• Primary Completion (Estimated): June 1, 2026
• Study Completion (Estimated): July 1, 2026

Study Registration Dates

• First Submitted: November 24, 2025
• First Submitted That Met QC Criteria: November 24, 2025
• First Posted (Actual): December 4, 2025

Study Record Updates

• Last Update Posted (Actual): April 3, 2026
• Last Update Submitted That Met QC Criteria: April 1, 2026
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Keywords: Microbiome; Abemaciclib; Gastrointestinal microbiome; Microbiome biomarkers; Hormone receptor-positive breast cancer; Drug-induced diarrhea; Abemaciclib-related diarrhea
• Additional Relevant MeSH Terms: Neoplasms by Site; Neoplasms; Skin Diseases; Breast Diseases; Skin and Connective Tissue Diseases; Breast Neoplasms
• Other Study ID Numbers: LLHBCH2025YN-088

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data (IPD) that underlie the results reported in this study will not be shared publicly. The decision is based on the following considerations: to protect patient privacy and confidentiality, as the data contain sensitive clinical and genomic information; the informed consent obtained from participants does not include provisions for public data sharing; and the samples and data are collected under a specific ethical approval that limits their use to this research protocol. Summary results and aggregated data will be made available through publication.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: Yes