Top Line: Whether to include or omit the internal mammary lymph nodes is a question that seems to frequently elude a simple answer.
The Study: The recent KROG 08-06 trial did not detect a significant difference in disease free survival at 7 years after regional nodal irradiation (RNI) with or without inclusion of the internal mammary nodes. However, the small differences in outcomes were of a similar magnitude to those of the much larger EORTC 22922 and MA.20 trials. Fifteen year results of the former showed a continued reduction in breast cancer recurrence and breast cancer mortality, but not overall survival. Another study that has contributed to this conversation is the Danish Internal Mammary Node Study. In this nationwide prospective cohort study, >3000 women with node positive breast cancer treated with RNI between 2003 and 2007 received IMN coverage if the tumor was on the right or IMN omission if the tumor was on the left. With long term follow up, overall survival at 15 years was significantly higher among those with right-sided tumors who received IMN by nearly 5% ( 60.1% v 55.4%). Furthermore, breast cancer mortality was lower (31.7% v 33.9%), and the rate of distant recurrence was lower with right sided IMN coverage (35.6% v 38.6%). The paper includes a very informative figure comparing Kaplan-Meier estimates of cumulative mortality with or without IMN coverage. While this trial helps confirm a small but detectable difference in breast cancer mortality and even survival with IMN coverage, one may wonder if cardiac events from left-sided IMN coverage could reduce the magnitude of benefit seen here.
TBL: Including internal mammary nodes for right sided, node positive breast cancer reduces distant metastasis and breast cancer mortality and improves overall survival compared to left sided disease with no IMN coverage. | Thorsen, J Clin Oncol 2022