The effect of tumor size on nodal disease burden in clinically node negative breast cancer.

e12575 Background: Randomized trials have shown no difference in outcomes for cT1-2N0 breast cancer patients with 1-2+ sentinel lymph nodes (SLNs) undergoing sentinel lymph node biopsy (SLNB) alone compared to axillary dissection (ALND). No studies have yet evaluated whether these results can be applied to cT3N0 patients. Our objective was to evaluate nodal burden in cT3N0 compared to cT1-2N0 patients. Methods: Patients with cT1-3N0 breast cancer undergoing upfront surgery were identified from the National Cancer Database (NCDB) from 2012 through 2017. Analysis was limited to those with ≥ 3 lymph nodes (LNs) retrieved. Clinical and pathologic characteristics were examined using Wilcoxon Rank sum tests, Chi square, or Fisher’s exact tests. Univariate and multivariable logistic regression analyses were performed to examine characteristics associated with increased nodal burden (≥ 3 +LNs). Results: During the study period, we identified 198,137 cN0 patients with ≥ 3 LNs retrieved, of which 191,672 (97%) were cT1-2 and 6,465 (3%) were cT3. Most patients had ductal histology (83%) and ER+/HER2- subtype (83%). Of cT1-2 patients, 7% (13,902/191,672) had ≥ 3 +LNs compared to 28% (1,791/6,465) of cT3 patients. Among patients with ≥ 3 +LNs, the majority (91%) underwent ALND with a median of 14 (interquartile range [IQR] 9,19) LNs retrieved. Of these patients, cT3 disease was associated with an increased number of +LNs compared to cT1-2 disease (median [IQR], 6 [4,10] vs. 4 [3,7], p<0.01). On multivariable analysis, invasive lobular carcinoma (ILC) (OR 2.11, 95% CI 1.34-3.30), lymphovascular invasion (LVI) (OR 5.22, 95% CI 4.43-6.16), and pathological tumor size > 8 cm (OR 2.76, 95% CI 2.16-3.53) were independently associated with ≥ 3 +LNs in cT3 patients. Triple-negative breast cancer (TNBC) was associated with lower odds of ≥ 3 +LNs (OR 0.50, 95% CI 0.36-0.68). In those with tumors 5-8 cm in size, 364 (27%) of 1,363 patients with IDC had ≥ 3 +LNs, compared to 152 (48%) of 315 patients with ILC. Conclusions: cT3N0 patients have increased nodal burden compared to cT1-2N0 patients. Caution should be used in extrapolating guidelines for cT1-2N0 patients to high-risk cT3N0 patients with large tumors, LVI, and lobular histology.[Table: see text]