The randomized phase III trial, known as HypoMast-IMNI, tested whether hypofractionated radiation combined with internal mammary node irradiation could match the tumor control and survival rates of conventional schedules without escalating harm. Researchers found no significant differences between the two treatment arms across primary and secondary endpoints, opening the door to shorter hospital visits for patients requiring intensive adjuvant therapy.
By News-USA.today Staff AnalystResearchers Enrolled Women Aged 18 to 70 Meeting Specific Criteria
Investigators enrolled women aged 18 to 70 who underwent mastectomies with negative margins and axillary lymph node dissections removing at least 10 nodes. Participants presented with pathologic T1-4N2-3 or T3-4N1 disease, or T1-2N1 disease alongside at least one high-risk indicator. Those markers included being younger than 40, harboring a histologic grade 3 tumor, showing lymphovascular invasion, testing hormone receptor-negative, or demonstrating HER2 overexpression. Patients who received neoadjuvant chemotherapy were excluded from the study.
Baseline characteristics remained evenly balanced across both arms. The median patient age stood at 49 years, ranging from 21 to 70. Most participants presented with pT2 disease at 62.8% and pN1 nodal status at 57.1%, while no patients exhibited pT4 disease. Hormone receptor-positive/HER2-negative disease accounted for 52.5% of the cohort, hormone receptor-positive/HER2-positive made up 17.1%, hormone receptor-negative/HER2-positive comprised 15.7%, and hormone receptor-negative/HER2-negative represented 14.7%. Nearly the entire cohort—99.9%—received adjuvant chemotherapy.
Hypofractionated and Conventional Radiation Show Comparable Five-Year Survival Rates
Locoregional recurrence served as the primary endpoint, while secondary measures tracked distant metastasis-free survival, breast cancer recurrence-free survival, disease-free survival, overall survival, and treatment-related toxicity. Five-year distant metastasis-free survival hit 92.3% in the hypofractionated arm versus 92.7% in the conventionally fractionated arm. Five-year breast cancer recurrence-free survival reached 91.8% and 92.3% respectively.
Disease-free survival at five years registered at 88.5% for hypofractionated radiation and 89.4% for conventional treatment. Overall survival at the five-year mark stood at 95.1% compared to 96.1%. Subgroup analyses based on T and N stage, molecular subtype, age, histology, and grade confirmed consistent locoregional recurrence effects.
| Outcome Metric (5-Year) | Hypofractionated Radiation | Conventionally Fractionated Radiation |
|---|---|---|
| Distant Metastasis-Free Survival | 92.3% | 92.7% |
| Breast Cancer Recurrence-Free Survival | 91.8% | 92.3% |
| Disease-Free Survival | 88.5% | 89.4% |
| Overall Survival | 95.1% | 96.1% |
Safety data showed no grade 4 toxicities or treatment-related deaths in either group. Hypofractionated radiation lowered the incidence of acute skin toxicities, posting reduced rates of grade 1 to 2 skin pruritus at 26.7% versus 35.2%, and skin pain at 7.7% compared to 23.3%. Late grade 1 to 2 hyperpigmentation occurred less frequently in the experimental arm as well, at 21.8% versus 27.2%.
Other adverse events remained comparable between the two cohorts. Grade 2 radiation pneumonitis affected 2.0% of the hypofractionated group and 2.1% of the conventional group, while grade 2 pulmonary fibrosis appeared in 1.3% of patients in both arms. Lymphedema, rib fractures, shoulder dysfunction, and brachial plexus injuries occurred at similar rates. Among 133 patients who underwent breast reconstruction, the shorter regimen did not elevate complication risks.
Authors Note Design Constraints and Need for Longer Follow-Up
The independent data and safety monitoring committee recommended the final analysis in 2025 because event rates ran lower than initial projections. Authors of the study noted several limitations, including the exclusion of patients who received neoadjuvant chemotherapy, the use of axillary lymph node dissection in all patients, a single-center design, and an underrepresentation of patients with N3b or N3c disease.
Longer follow-up remains necessary to fully capture late-onset toxicities, particularly potential cardiac impacts resulting from internal mammary node irradiation. X. Wang, X. Zhang, X.
