Sentinel and non-sentinel lymph node metastases in patients with microinvasive breast cancer: a nationwide study

PurposeTo determine the incidence and risk factors of sentinel lymph node (SN) and non-SN metastases in patients with microinvasive breast cancer (MIBC, T1(mic)). This to identify MIBC patients in whom axillary staging can be safely omitted.MethodsThe Danish Breast Cancer Group database was used to identify a total of 409 women with breast cancer1mm who underwent sentinel lymph node biopsy (SLNB) between 2002 and 2015. After validation, 233 patients were eligible for the analysis. The incidence rates of SN and non-SN metastases were determined. The associations between clinicopathological variables and a positive SN [pN1, pN1mi, or pN0(i+)] were analyzed using univariate and multivariate designs.ResultsOf 233 patients with MIBC, only 9 (3.9%) had SN macrometastases. An additional 18 (7.7%) and 23 (9.9%) had SN micrometastases and isolated tumor cells (ITCs), respectively. Of patients with SN macrometastases, two (22.2%) had non-SN macrometastases. In the adjusted analysis, a positive SN was associated with younger age (P=0.0001) and a positive human epidermal growth factor 2 receptor (HER2) status (P=0.03).ConclusionsThe low incidence of SN macrometastases<4% suggests omission of axillary staging in MIBC patients without staging at primary surgery, especially in older (50years) HER2(-) patients. Still, the relatively high proportion of patients with non-SN macrometastases indicates that axillary treatment might be considered in SN positive patients, especially in younger HER2(+) MIBC patients.