The SOUND (Sentinel Node vs Observation After Axillary Ultra-Sound) trial was a prospective noninferiority phase 3 randomized clinical trial suggesting that omission of axillary surgery was noninferior to SLNB in patients with small breast cancer and a negative result on ultrasonography of the axillary lymph nodes.

In the study conducted by Gentilini et al, a total of 1463 women of any age with breast cancer up to 2 cm and a negative preoperative axillary ultrasonography result were enrolled and randomized on a 1:1 ratio to receive SLNB (SLNB group) or no axillary surgery (no axillary surgery group).

The primary end point of the study was distant disease–free survival (DDFS) at 5 years, analyzed as intention to treat. 5-year DDFS was 97.7% in the SLNB group and 98.0% in the no axillary surgery group (p=0.67; noninferiority p=0.2). A total of 12 (1.7%) locoregional relapses, 13 (1.8%) distant metastases, and 21 (3.0%) deaths were observed in the SLNB group, and 11 (1.6%) locoregional relapses, 14 (2.0%) distant metastases, and 18 (2.6%) deaths were observed in the no axillary surgery group.

How might these results affect your recommendations regarding omission of RT for those patients >65 as in the PRIME II trial who did have a SLN biopsy?