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

BackgroundThe 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. MethodsPatients 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. ResultsPatients 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. ConclusionsPatients 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. Source of fundingThe authors declare no conflicts of interest. The Sk[a]ne County Councils Research and Developmental Foundation, the Governmental Funding of Clinical Research within the National Health Service (ALF), the Swedish Cancer Society, the Erling Persson Family Foundation, Kronoberg County Councils Research and Development Foundation, The Cancer Foundation Kronoberg, The Swedish Research Council and The Swedish Breast Cancer Association. The funding agencies had no role in study design or interpretation of data. Previous communicationPreliminary findings were published as part of Ulrik Narbes doctoral thesis. Trial registrationISRCTN registry: ISRCTN14341750