Internal Mammary Node Irradiation After Neoadjuvant Systemic Therapy for Breast Cancer (IMN-Neo)

November 3, 2026 updated by: Mahidol University

Internal Mammary Node Irradiation Versus Omission of Internal Mammary Node Irradiation in Breast Cancer Treated With Neoadjuvant Systemic Therapy: A Phase III Multicenter Randomized Trial

This multicenter randomized controlled trial evaluates whether internal mammary node irradiation (IMNI) improves oncologic outcomes in patients with breast cancer who have residual pathologically positive lymph nodes after neoadjuvant systemic therapy.

Eligible participants will be randomly assigned in a 1:1 ratio to receive locoregional radiotherapy either with or without irradiation of the internal mammary lymph nodes. The primary outcome is disease-free survival. Secondary outcomes include overall survival, breast cancer mortality, locoregional recurrence-free survival, distant metastasis-free survival, and treatment-related toxicity, particularly cardiac and pulmonary toxicity.

A total of 1,760 participants are planned to be enrolled across multiple centers in Thailand.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

Regional nodal irradiation is an established component of adjuvant radiotherapy for selected patients with node-positive breast cancer. However, the additional benefit of internal mammary node irradiation (IMNI) remains uncertain, particularly in patients receiving contemporary neoadjuvant systemic therapy. Although previous randomized trials have demonstrated potential oncologic benefits of regional nodal irradiation incorporating IMNI, most were conducted in patients undergoing upfront surgery, before the widespread use of modern systemic treatments. Consequently, the benefit-risk balance of IMNI in patients with residual nodal disease after neoadjuvant systemic therapy remains unclear.

IMN-Neo is a phase III, multicenter, randomized, open-label superiority trial designed to evaluate whether the addition of IMNI to standard locoregional radiotherapy improves oncologic outcomes in patients with residual pathologically positive axillary lymph nodes following neoadjuvant systemic therapy.

Participants will be randomized in a 1:1 ratio using computer-generated mixed block randomization, stratified by pathological nodal stage, method of axillary evaluation, primary tumor location, and breast cancer molecular subtype. Randomization will be performed at the time of radiotherapy simulation.

Both treatment groups will receive radiotherapy to the breast or chest wall and regional lymph nodes according to protocol-defined target delineation and dose constraints. The experimental group will additionally receive irradiation of the internal mammary lymph nodes, encompassing the first through third intercostal spaces, whereas the control group will undergo intentional omission of IMNI. Three-dimensional conformal radiotherapy or more advanced techniques will be used, with deep inspiration breath-hold permitted to minimize radiation exposure to surrounding normal tissues.

Participants will undergo scheduled clinical follow-up to assess disease recurrence, survival, and treatment-related adverse effects. Particular attention will be given to cardiac and pulmonary toxicity because of the potential increase in radiation exposure associated with IMNI.

An independent Data and Safety Monitoring Board will oversee participant safety and trial conduct. A prespecified interim efficacy analysis will be performed after approximately 50% of the required primary endpoint events have occurred, with additional monitoring for unexpected oncologic harm and serious treatment-related toxicity.

The trial aims to provide prospective evidence to guide individualized decision-making regarding IMNI in patients with residual nodal disease following contemporary neoadjuvant systemic therapy.

Study Type

Interventional

Enrollment (Estimated)

1760

Phase

  • Phase 3

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

  • Thailand
      • Bangkok, Thailand
        • Chulabhorn Hospital
        • Contact:
        • Sub-Investigator:
          • Areeya Tinsurawattana, MD
      • Chon Buri, Thailand
        • Chonburi Cancer Hospital
        • Contact:
      • Chon Buri, Thailand
        • Vibharam Amata Nakorn Cancer Hospital
        • Contact:
      • Lopburi, Thailand
        • Lop Buri Cancer Hospital
        • Contact:
      • Nakhon Pathom, Thailand
        • Synphaet Hospital Nakhon Pathom
        • Contact:
      • Nakhon Si Thammarat, Thailand
        • Maharaj Nakhon Si Thammarat Hospital
        • Contact:
      • Ratchaburi, Thailand
        • Ratchaburi Hospital
        • Contact:
      • Samut Sakhon, Thailand
        • Metropolitan Hospital Tha Chalom, Samut Sakhon Hospital
        • Contact:
    • Bangkok Noi
      • Bangkok, Bangkok Noi, Thailand, 10700
        • Siriraj Hospital
        • Contact:
        • Principal Investigator:
          • Tanun Jitwatcharakomol, MD
        • Sub-Investigator:
          • Pittaya Dankulchai, MD
        • Sub-Investigator:
          • Janjira Petsuksiri, MD
        • Sub-Investigator:
          • Chinnavuth Vatanashevanopakorn, MD
        • Sub-Investigator:
          • Pongpop Tuntapakul, MD
        • Sub-Investigator:
          • Wiwatchai Sittiwong, MD
        • Sub-Investigator:
          • Ratchapas Romrattaphan, MD
        • Sub-Investigator:
          • Krittee Chesdachai, MD

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

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

Female

Description

Inclusion Criteria:

  • Histologically confirmed breast cancer with pathologically proven lymph node positivity after neoadjuvant systemic therapy.
  • Received neoadjuvant chemotherapy and/or targeted therapy and/or immunotherapy before surgery.
  • Underwent either breast-conserving surgery or mastectomy with lymph node evaluation and is planned to receive adjuvant locoregional radiotherapy.
  • Planned treatment with three-dimensional conformal radiotherapy (3D-CRT) or a more advanced radiotherapy technique.
  • Female ≥ 18 years

Exclusion Criteria:

  • Clinical or radiologic evidence of internal mammary lymph node involvement of any size.
  • Inflammatory breast cancer.
  • Bilateral breast cancer.
  • Multiple primary malignancies, except basal cell carcinoma and premalignant gynecologic lesions including CIN, HSIL, LSIL, VIN, and VAIN.
  • Prior chest irradiation.
  • Disease progression before radiotherapy.
  • Metastatic disease (M1) according to the AJCC 8th edition.

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

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: IMNI Group

Participants will receive adjuvant locoregional radiotherapy including irradiation of the internal mammary lymph nodes.
Radiation: Locoregional Radiotherapy With Internal Mammary Node Irradiation

Adjuvant locoregional radiotherapy to the breast or chest wall and regional lymph nodes, including the internal mammary lymph nodes. Allowed dose-fractionation schedules include 50 Gy in 25 fractions, 42.5 Gy in 16 fractions, or 40 Gy in 15 fractions, according to the study protocol.

Other Names:
  • IMNI Group
Active Comparator: Non-IMNI Group

Participants will receive adjuvant radiotherapy to the breast or chest wall and regional lymph nodes without irradiation of the internal mammary lymph nodes.
Radiation: Locoregional Radiotherapy Without Internal Mammary Node Irradiation

Adjuvant locoregional radiotherapy to the breast or chest wall and regional lymph nodes, with intentional omission of the internal mammary lymph nodes. Allowed dose-fractionation schedules include 50 Gy in 25 fractions, 42.5 Gy in 16 fractions, or 40 Gy in 15 fractions, according to the study protocol.

Other Names:
  • Non-IMNI Group

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Disease-Free Survival (DFS)
Time Frame: From randomization through 5 years

Disease-free survival is defined as the time from randomization to the first occurrence of locoregional recurrence, distant metastasis, or death from any cause, whichever occurs first.
From randomization through 5 years

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Overall Survival (OS)
Time Frame: Up to 5 years after randomization

Overall survival is defined as the time from randomization to death from any cause.
Up to 5 years after randomization
Breast Cancer Mortality
Time Frame: Up to 5 years after randomization

Breast cancer mortality is defined as the time from randomization to death attributable to breast cancer.
Up to 5 years after randomization
Locoregional Recurrence-Free Survival (LRFS)
Time Frame: Up to 5 years after randomization

Locoregional recurrence-free survival is defined as the time from randomization to the occurrence of locoregional recurrence.
Up to 5 years after randomization
Distant Metastasis-Free Survival (DMFS)
Time Frame: Up to 5 years after randomization

Distant metastasis-free survival is defined as the time from randomization to the occurrence of distant metastasis.
Up to 5 years after randomization
Incidence and Severity of Cardiac Toxicity Assessed Using RTOG/EORTC Radiation Morbidity Scoring Criteria
Time Frame: Last week of radiotherapy, then at 1, 3, and 6 months, and every 6 months through 2 years

Acute cardiac toxicity will be assessed using the RTOG Acute Radiation Morbidity Scoring Criteria, while late cardiac toxicity will be assessed using the RTOG/EORTC Late Radiation Morbidity Scoring Schema. Toxicity will be graded from 0 (no toxicity) to 5 (death related to toxicity). The incidence and severity of cardiac toxicity will be compared between treatment groups.
Last week of radiotherapy, then at 1, 3, and 6 months, and every 6 months through 2 years
Incidence and Severity of Pulmonary Toxicity Assessed Using RTOG/EORTC Radiation Morbidity Scoring Criteria
Time Frame: Last week of radiotherapy, then at 1, 3, and 6 months, and every 6 months through 2 years

Acute pulmonary toxicity will be assessed using the RTOG Acute Radiation Morbidity Scoring Criteria, while late pulmonary toxicity will be assessed using the RTOG/EORTC Late Radiation Morbidity Scoring Schema. Toxicity will be graded from 0 (no toxicity) to 5 (death related to toxicity). The incidence and severity of pulmonary toxicity will be compared between the two treatment groups.
Last week of radiotherapy, then at 1, 3, and 6 months, and every 6 months through 2 years

Collaborators and Investigators

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

Sponsor

Mahidol University

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

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 (Estimated)

July 1, 2027

Primary Completion (Estimated)

July 1, 2032

Study Completion (Estimated)

July 1, 2036

Study Registration Dates

First Submitted

October 28, 2026

First Submitted That Met QC Criteria

November 3, 2026

First Posted (Actual)

November 4, 2026

Study Record Updates

Last Update Posted (Actual)

November 4, 2026

Last Update Submitted That Met QC Criteria

November 3, 2026

Last Verified

October 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 587/2569(IRB2)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

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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