Risk factors for non-sentinel lymph node metastases in patients with breast cancer. The outcome of a multi-institutional study

Background: In this multi-institutional prospective study, we evaluated whether we could identify risk factors predictive for non-sentinel lymph node (non-SN) metastases in breast cancer patients with a positive sentinel lymph node (SN). Methods: In this multi-institutional study, 541 eligible breast cancer patients were included prospectively. Results: The occurrence of non-SN metastases was related to the size of the SN metastasis (P = .02), primary tumor size (P = .001), and lymphovascular invasion (P = .07). The adjusted odds ratio was 3.1 for SN micro-metastasis compared with SN isolated tumor cells, 4.0 for SN macro-metastasis versus SN isolated tumor cells, 3.1 for tumor size (> 3.0 cm compared with <= 3.0 cm), and 2.0 for lymphovascular invasion (yes versus no). There were no positive non-SNs when the primary tumor size was <= 1.0 cm (n = 24) [95% confidence interval (95% CI) 0%-14.0%]. The proportion of positive non-SNs ranged in a prognostic logistic regression model from 9.7% (95% CI 4.0%-23.0%) for patients with SN isolated tumor cells, tumor size of 1.1-3.0 cm, and without vessel invasion, to 72.6% (95% CI 47.0%-89.0%) for patients with SN macro-metastasis, tumor size > 3.0 cm, and with vessel invasion. Conclusion: We identified three predictive factors for non-SN metastases in breast cancer patients with a positive SN: size of the SN metastasis; primary tumor size; and vessel invasion. We were not able to identify a specific group of patients with a positive SN in whom the risk for non-SN metastases was less than 5%.