Role of sentinel lymph node biopsy in patients with early breast cancer undergoing mastectomy.

BACKGROUND: The oncological non-inferiority of sentinel lymph node biopsy omission in patients with small, clinically and imaging node-negative (cN0/iN0) breast cancer has been demonstrated for patients undergoing breast-conserving surgery and adjuvant radiotherapy, but not for those undergoing mastectomy. This single-centre, retrospective cohort study compared nodal involvement and adjuvant therapy indications in these patients by use of mastectomy versus breast-conserving surgery. METHODS: Patients with cT1-T2, cN0/iN0, hormone receptor-positive/human epidermal growth factor receptor 2-negative early breast cancer who underwent upfront surgery including sentinel lymph node biopsy between January 2014 and December 2024 were included. Adjuvant therapy indications were estimated using monarchE (abemaciclib), NATALEE (ribociclib), TAILORx and RxPONDER (chemotherapy), and MA.20 and EORTC22922/10925 (nodal irradiation) eligibility criteria. Multivariable logistic regression models identified factors associated with nodal involvement and adjuvant treatment indications. RESULTS: Among 454 patients, 145 (31.9%) underwent mastectomy who more frequently had multifocal tumours (23.5% versus 9.7%), lobular subtype (21.4% versus 11.3%), and grade 2-3 differentiation (73.8% versus 63.8%) compared with those who underwent breast-conserving surgery. Neither nodal involvement (18.6% versus 14.9%; P = 0.149) nor missed indications for adjuvant abemaciclib (7.6% versus 6.1%; P = 0.550), ribociclib (9.7% versus 7.8%; P = 0.586), and nodal irradiation (4.8% versus 4.5%; P = 1.000) differed between patients who underwent mastectomy or breast-conserving surgery. Lymphovascular invasion was independently associated with nodal involvement (odds ratio 6.8, 95% confidence interval 3.7 to 12.8; P < 0.001) and adjuvant treatment indications (CDK4/6 inhibitors: odds ratio 5.1, 2.6 to 10.1; P < 0.001; nodal irradiation: odds ratio 7.1, 3.6 to 14.4; P < 0.001), whereas type of surgery was not. CONCLUSIONS: In patients with cT1-T2, cN0/iN0, hormone receptor-positive/human epidermal growth factor receptor 2-negative breast cancer, type of breast surgery was not associated with nodal involvement and adjuvant therapy.