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

To 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.

The Danish Breast Cancer Group database was used to identify a total of 409 women with breast cancer ≤ 1 mm 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.

Of 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).

The low incidence of SN macrometastases < 4% suggests omission of axillary staging in MIBC patients without staging at primary surgery, especially in older (≥ 50 years) 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.