Study to Understand Relationship Between Gut Health and Toxicities of Hormonal Breast Cancer Treatment (GEMMA)

Prospective Evaluation of the Gut Microbiome and a Pilot Dietary Intervention in Patients With HR+/HER2- Breast Cancer Receiving Abemaciclib (GEMMA)

This study will be conducted in 2 sequential parts. The first part will be a prospective, observational study. This will be followed by a small interventional, pilot study involving use of fiber supplement (chia seeds). The study aims to evaluate the relationship between the gut microbiome (a diverse ecosystem of microorganisms that affects your health and well-being) and treatment-related gastrointestinal toxicities in patients with HR+/HER2- breast cancer receiving abemaciclib plus endocrine therapy.

Study Overview

• Status: Not yet recruiting
• Conditions: Breast Cancer
• Intervention / Treatment: Other: Stool Sampling; Other: Chia Seeds

• Study Type: Interventional
• Enrollment (Estimated): 20
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Clinical Trials Intake; Phone Number: 855-702-8222; Email: cancerclinicaltrials@bsd.uchicago.edu
• Study Contact Backup: Name: Rita Nanda; Email: rnanda@bsd.uchicago.edu

Study Locations

• United States
  • Illinois
    • Chicago, Illinois, United States, 60637
      • The University of Chicago Medicine Comprehensive Cancer Center
      • Principal Investigator: Rita Nanda
      • Contact: Clinical Trials Intake; Phone Number: 855-702-8222; Email: cancerclinicaltrials@bsd.uchicago.edu

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Be willing and able to provide written informed consent for the trial
• Be a male or female subject 18 years of age on day of signing informed consent.
• Histologically proven infiltrating carcinoma of the breast on core needle biopsy that is:

HER2 negative in primary tumour pre-treatment by local pathology assessed according current American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines: In situ hybridization non-amplified (ratio of HER2 to CEP17 < 2.0 or single probe average HER2 gene copy number < 4 signals/cell), OR Immunohistochemistry (IHC) 0 or IHC 1+.

• Estrogen receptor (ER) and progesterone receptors (PR) positive in primary tumour pre-treatment defined as >1% of cells expressing hormonal receptors via IHC analysis by local laboratory assessment.
• Planned to undergo standard of care therapy with abemaciclib and endocrine therapy, in the adjuvant or metastatic setting (Part 1) or the adjuvant setting (Part 2).
• Be willing to provide mandatory stool samples at baseline and on treatment.
• The Eastern Cooperative Oncology Group (ECOG) 0-2

Exclusion Criteria:

• Patients who are pregnant or breast-feeding
• Current use of any investigational agents
• Uncontrolled Ulcerative Colitis, Crohn's Disease, Malabsorption syndrome or any disease significantly affecting gastrointestinal function
• History or current evidence of any condition, therapy, lab abnormality or other circumstance that in the opinion of the investigator might expose the subject to risk by participating in the trial, confound the results of the trial, or interfere with the subject's participation for the full duration of the trial.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Supportive Care
• Allocation: Non-Randomized
• Interventional Model: Sequential Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Observational Cohort; Enrolled patients with early or advanced HR+/HER2- breast cancer starting abemaciclib as per standard of care to characterize the baseline composition and longitudinal dynamics of the gut microbiome before and during treatment. Stool samples will be collected continuously using the GutLab platform, alongside clinical toxicity assessments, with a focus on identifying microbial signatures associated with the development and severity of diarrhea. No intervention will be administered.	Other: Stool Sampling; Stool samples will be collected continuously (during as many bowel movements as possible) using the GutLab device (BiomeSense, Inc.).
Experimental: Dietary Intervention Cohort; Enrolled patients with early-stage HR+/HER2- breast cancer. A 2-week chia seed intervention will be administered prior to initiation of abemaciclib. The goal of this high fiber intervention is to favorably modulate the gut microbiome by supporting a more diverse microbiome and reducing the risk of inflammation and dysbiosis.	Other: Stool Sampling; Stool samples will be collected continuously (during as many bowel movements as possible) using the GutLab device (BiomeSense, Inc.).; Other: Chia Seeds; In the Fiber Study cohort (Part 2), participants will be advised to consume a standardized daily serving of chia seeds (25g/day) and provided with guidance on how to integrate this into their usual diet.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Stool Sampling Feasibility	Proportion of enrolled participants who provide serial stool samples during the baseline and on-treatment periods, as recorded by device data and study records.	2 years

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Baseline Microbiome-Diarrhea Associations	Correlation between baseline gut microbiome composition and incidence of grade ≥2 diarrhea during abemaciclib therapy, as defined by CTCAE v6.0.	2 years
Microbiome Dynamics and Diarrhea	Correlation between longitudinal changes in gut microbiome composition during abemaciclib therapy and incidence and severity of grade ≥2 diarrhea, as defined by CTCAE v6.0.	2 years

Collaborators and Investigators

• Sponsor: University of Chicago
• Investigators: Principal Investigator: Rita Nanda, University of Chicago

Study record dates

Study Major Dates

• Study Start (Estimated): December 27, 2026
• Primary Completion (Estimated): May 3, 2030
• Study Completion (Estimated): May 3, 2030

Study Registration Dates

• First Submitted: March 2, 2026
• First Submitted That Met QC Criteria: April 22, 2026
• First Posted (Actual): April 27, 2026

Study Record Updates

• Last Update Posted (Actual): May 4, 2026
• Last Update Submitted That Met QC Criteria: April 28, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Neoplasms by Site; Neoplasms; Skin Diseases; Breast Diseases; Skin and Connective Tissue Diseases; Breast Neoplasms
• Other Study ID Numbers: IRB25-2098

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No