Can patients with biopsy-diagnosed DCIS safely spare sentinel lymph node biopsy (SLNB)?

e12583 Background: While the guidelines generally recommend that most patients with biopsy-diagnosed breast ductal carcinoma in situ (DCIS) can be spared from axillary staging if receiving breast conserving surgery, the percentage of such patients received SLNB is still as high as 50-70%. SOUND trial recently provides some low risk invasive breast cancer patients with the option of omitting SLNB, further highlighting the necessity of omitting SLNB in DCIS patients. This study aimed to retrospectively analyze the chance of turning into invasive cancer and lymph node metastasis in the patients who are diagnosed as DCIS by biopsy. Methods: Preoperative biopsy-diagnosed breast pure DCIS patients between 2011-2023 were retrospectively reviewed in Sun Yat-sen Memorial Hospital. Patients with axilla staging were grouped by pathology status (LN- versus LN+). Differences were compared using either t test or chi-squared test. Multi-variate logistic regression model was conducted to stratify the risk for LN metastasis. Results: 1193 patients were eligible for analysis, of whom 51.8% turned invasive breast cancer (IBC) in post-surgery pathology. 42% and 81% of IBCs were only T1 mi and less than 1cm foci (T1a,b) respectively. 1161 (97.3%) patients had available axilla LN information and their axillary metastasis rate was 7.1% (0.9% and 12.5% in DCIS and IBC). Only 22 (1.9%) or 15 (1.3%) patients had ≥ 3 or 4 positive LN involved. Multi-variate analysis identified four risk factors associated with LN metastasis: ultrasound suspicious lymph node (OR=2.22, 95%CI: 1.21-4.07), tumor size (>2cm vs ≤2cm: OR=2.85, 95%CI:1.10-7.42), biopsy method (core biopsy vs excision: OR=7.04, 95%CI:1.60-31.25) and necrosis (OR=2.20, 95%CI: 1.23-3.94). Among 440 patients with excision biopsy, only 1.4% had LN involved. In the other 721 patients diagnosed by core biopsy, the LN metastasis rate of patients who had 0,1,2 and 3 risk factors were 3.6%, 6%, 21% and 29.5%, respectively. Based on the number of risk factors patients were stratified to low risk (having 0-1 risk factor) and high risk (having ≥2 risk factors), with low risk patients having only 5.4% LN metastasis. Conclusions: Although the patients diagnosed with preoperative pure DCIS had a high chance of upgrading to invasive cancer, only 7.1% of them had lymph node metastasis. 98% of them are Z0011-eligible and 40% of them are SOUND-eligible if they receive breast conserving surgery, indicating the futility of axillary staging in these patients. We identified four independent risk factors for LN metastasis (suspicious lymph node on US, tumor size, biopsy method and necrosis). Even in the patients who received mastectomy, if they have only 0-1 risk factors, SLNB can still be safely omitted.