Internal Mammary Node Irradiation May Benefit Some Breast Cancer Patients

In In The News by Barbara Jacoby

By: Leah Lawrence


Internal mammary node irradiation (IMNI) may benefit patients with node-positive breast cancer who have mediocentrally located tumors, according to phase 3 results published in JAMA Oncology.

However, the study also suggests that IMNI does not significantly benefit patients with node-positive breast cancer overall.

This phase 3 trial ( Identifier: NCT04803266) was conducted to determine if the inclusion of IMNI in regional nodal irradiation improved disease-free survival (DFS).

The study included 735 patients with node-positive breast cancer treated at 13 hospitals in South Korea. The patients’ median age was 48 years (range, 28-77 years), 58.2% had lateral tumors, and 91.6% had ductal histology.

Half of patients (49.9%) had undergone breast-conserving surgery, 95.6% had received taxane-containing chemotherapy, and 67.2% had received hormone therapy.

Patients were randomly assigned to receive radiotherapy with IMNI (n=362) or without IMNI (n=373). The median follow-up was 100.4 months.


The 7-year DFS rate was not significantly different between patients without and with IMNI — 81.9% and 85.3%, respectively (hazard ratio [HR], 0.80; 95% CI, 0.57-1.14; P =.22).

Although there was no significant difference in 7-year DFS, the trial “raised the possibility of an improvement,” the researchers wrote. They speculated that the reason the DFS improvement seen with IMNI did not reach statistical significance might be “a lower-than-anticipated event rate with a corresponding loss of statistical power.”

Furthermore, an ad hoc subgroup analysis showed significantly higher DFS with IMNI in patients with mediocentrally located tumors. Here, the 7-year DFS was 81.6% without IMNI and 91.8% with IMNI (HR, 0.42; 95% CI, 0.22-0.82; P =.008).

Also in patients with mediocentrally located tumors, the 7-year breast cancer mortality rate was twice as high without IMNI as with IMNI — 10.2% and 4.9%, respectively (HR, 0.41; 95% CI, 0.17-0.99; P =.04).

“[W]e believe that the benefit of IMNI was affected by the tumor location and that patients with mediocentrally located tumors can be considered to receive IMNI when performing regional nodal irradiation,” the researchers wrote. “However, the subgroup analysis was not preplanned; thus, these findings should be interpreted with caution.”


Kim YB, Byun HK, Kim DY, et al. Effect of elective internal mammary node irradiation on disease-free-survival in women with node-positive breast cancer. A randomized phase 3 clinical trial. JAMA Oncol. Published online October 25, 2021. doi:10.1001/jamaoncol.2021.6036