The St. Gallen 2019 Guidelines understages the Axilla in Lobular Breast Cancer – a Population-Based Study

Abstract

Background The St. Gallen 2019 guidelines recommend omission of completion axillary lymph node dissection (cALND) in breast cancer patients with 1-2 sentinel lymph node (SLN) metastases regardless of histopathology. Concurrently, adjuvant chemotherapy is endorsed for luminal A-like disease with ≥4 axillary lymph node (ALN) metastases. We aimed to estimate the proportion of patients with invasive lobular cancer (ILC) and invasive ductal cancer of no special type (NST) and 1-2 SLN metastases for whom cALND would indicate need of adjuvant chemotherapy. Methods Patients with ILC and NST histopathology undergoing primary surgery 2014-2017 were identified in the Swedish National Quality Breast Cancer register. After exclusion of patients with incongruent or missing data, 1886 patients who fulfilled the St. Gallen 2019 criteria for cALND omission were included in the study cohort. Results Patients with ILC (n = 329) had a higher metastatic nodal burden and more often a luminal A-like subtype compared with NST patients (n = 1507). The prevalence of ≥ 4 ALN metastases was higher in ILC (31%) than in NST (15%), corresponding to an adjusted odds of 2.26 (95% CI 1.59-3.21). Luminal A-like breast cancers with ≥4 ALN metastases were overrepresented in ILC cases (52/281 (19%)) compared to NST cases (43/1299 (3%)), P<0.001. Conclusions Patients with ILC more often had a luminal A-like breast cancer with ≥4 ALN metastases compared with NST patients. Abstaining cALND in patients with luminal A-like ILC with 1-2 SLN metastases warrants future attention as it risks nodal understaging and hence undertreatment in one-fifth of these patients.