Analysis of sentinel lymph node biopsy and non-sentinel lymph node metastasis in invasive ductal and invasive lobular breast cancer: a nationwide cross-sectional study (CSBrS-001)

Background: Information regarding the implementation of sentinel lymph node biopsy (SLNB) in invasive lobular carcinoma (ILC) is scarce, and whether ILC patients with 1-2 positive sentinel lymph nodes (SLNs) can be omitted from axillary lymph node dissection (ALND) remains controversial. This study aimed to compare involvement of SLNs and non-SLNs between patients with invasive ductal carcinoma (IDC) and ILC. Methods: We retrospectively collected the clinical and pathological data of invasive breast cancer patients from 37 medical centers in China from January 2018 to December 2018. The number of resected SLNs, positive rate of SLNs, and non-SLNs metastasis were compared between patients with IDC and ILC. Results: A total of 6,922 patients were included, comprising 6,650 with IDC (96.1%) and 272 with ILC (3.9%). No difference was observed in the number of resected SLNs between patients with IDC and ILC (IDC: 4.0 +/- 1.9 vs. ILC: 3.9 +/- 1.6, P=0.352). The positive rate of SLNs was significantly higher in patients with IDC than that in patients with ILC (19.3% in IDC vs. 12.9% in ILC, P=0.008). The difference in positive rate of SLNs between IDC and ILC was mainly attributed to macro-metastasis. For patients with positive SLNs who received ALND, and those with 1-2 positive SLNs, the metastatic rate of non-SLNs in the ILC group was higher than that in the IDC group (for patients with positive SLNs: 50.0% in ILC vs. 39.9% in IDC, P=0.317; for patients with 1-2 positive SLNs: 45.4% in ILC vs. 34.8% in IDC, P=0.366), but the differences were not statistically significant. Conclusions: Patients with ILC had similar number of resected SLNs and lower positive rate of SLNs compared to those with IDC. In participants with 1-2 positive SLNs, the ILC group had an increased tendency for non-SLNs metastasis compared with the IDC group. Surgeons may need to be more cautious about omitting ALND for ILC patients with 1-2 positive SLNs.