Ultrasound May Help Early Breast Cancer Patients Avoid SLNB

Omitting axillary surgery completely in early breast cancer patients with a negative preoperative axillary ultrasound resulted in similar outcomes compared with sentinel lymph node biopsy (SLNB), and did not appear to affect adjuvant treatment decisions, a multinational phase III trial found.

Of over 1,400 women whose tumor was no more than 2 cm in diameter, the 5-year distant disease-free survival (DFS) was 97.7% in the group randomized to SLNB and 98.0% in the group assigned to no axillary surgery (HR 0.84, 90% CI 0.45-1.54, P=0.02 for noninferiority), reported researchers led by Oreste Davide Gentilini, MD, of the San Raffaele Scientific and Research Hospital in Milan.

For secondary endpoints, no differences at 5 years were seen for DFS, overall survival (OS), or the cumulative incidence of either distant or axillary recurrences.

Results of the study suggest that patients with small tumors and a negative ultrasound of the axillary lymph nodes “can be safely spared any axillary surgery when the lack of pathological information does not affect the postoperative treatment plan,” the investigators concluded in JAMA Oncology.

Despite concerns that the absence of pathological information gleaned from SLNB might affect subsequent decisions on adjuvant therapy, its use was not significantly different between groups, noted Gentilini and co-authors, confirming “the increasing pattern of guiding adjuvant treatment mostly through the use of biological parameters rather than clinicopathological variables.”

SLNB has been standard of care for early breast cancer patients receiving breast-conserving surgery, adjuvant radiotherapy, and medical treatment ever since the results of the landmark ACOSOG Z0011 trial, which showed no survival advantage with axillary lymph node dissection (ALND) versus SLNB for patients with up to two positive sentinel lymph nodes.

But according to Gentilini and colleagues, the absence of an advantage with ALND revealed in that trial raised two questions that led to their so-called SOUND study: “first, whether it is really necessary to perform surgical staging of axillary lymph nodes, and second, whether imaging might replace surgery for reliable staging of axillary lymph nodes.”

While the trial’s results were reassuring overall, “gaps remain,” said Seema Khan, MD, of the Northwestern University Feinberg School of Medicine in Chicago, in an editorial accompanying the study.

“Although a relatively simple and inexpensive test, the performance and interpretation of ultrasonography to triage patients into those with sonographically negative axillary nodes will vary across institutions,” Khan said, adding that institutional variations in accuracy are “a concern that is particularly relevant to the implementation of axillary ultrasonography for nodal evaluation in the setting of low axillary disease burden.”

As to the question of adjuvant treatment decisions, the “clinical application of these data requires multidisciplinary consultation, and there are situations where pathological nodal staging will clarify recommendations regarding intensity of adjuvant systemic therapy or decisions by the patient,” wrote Khan. “Similar decisions apply to the scope of radiotherapy (or to its omission).”

From 2012 to 2017, the SOUND (Sentinel Node vs Observation After Axillary Ultra-Sound) trial randomized 1,405 women with unifocal, clinical T1N0 breast cancer 1:1 to either SLNB (n=697) or no axillary surgery (n=708) at 25 centers in Italy, Switzerland, Spain, and Chile.

Women had a median age of 60 years, their median tumor size was 1.1 cm, and 87.8% had estrogen receptor-positive and HER2-nonoverexpressing cancers. In the SLNB group, 97 patients (13.7%) had positive axillary nodes (5.1% with micrometastases and 8.6% with macrometastases) and four patients (0.6%) had at least four positive lymph nodes.

Median follow-up for disease assessment was 5.7 years. Between the SLNB and no axillary surgery groups, respectively, investigators observed similar rates of locoregional relapses (1.7% vs 1.6%), distant metastases (1.8% vs 2.0%), and deaths (3.0% vs 2.6%).

Five-year outcomes between the SLNB group and no axillary surgery group were as follows:

• DFS 94.7% vs 93.9%, respectively
• OS: 98.2% vs 98.4%
• Incidence of distant metastases: 2.3% vs 1.9%
• Incidence of lymph node recurrences in the axilla: 0.4% vs 0.4%

As to whether ultrasound imaging might replace surgery in staging axillary lymph nodes, Gentilini and colleagues pointed out that in this study, ultrasound was able to rule out the presence of relevant nodal burden, “which might not have been identified with clinical evaluation alone.”

They noted that the 13.7% rate of nodal involvement in the SLNB group was lower than the rate seen in previous trials, and suggested this was due to the screening effect of the negative preoperative axillary ultrasound result necessary to enter the trial.

“Given the limited number of patients with macrometastases, the very low number of patients with extensive nodal involvement (0.6% with four or more positive nodes) in the axillary surgery group, and the extremely low cumulative incidence of axillary lymph node recurrence in the no axillary surgery group (0.4% at 5 years), the performance of ultrasonography can be considered clinically meaningful,” they concluded.

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