Background: Although internal mammary chain (IMC) metastases are an independent predictor of prognosis, collecting IMC sentinel nodes (SN) remains controversial. We sought to determine predictors for IMC nodal positivity and the role positive IMC-SNs have on changing staging and management. Methods: We reviewed a prospectively collected database (1997-2012) to identify patients who had IMC drainage detected on lymphoscintigraphy and underwent biopsy. Chi square tests and logistic regression models were used to determine trends and factors associated with IMC node positivity. Results: A total of 122 patients with cTis-T2cN0M0 breast cancer underwent IMC-SN biopsy. Mean age of the cohort was 53 years, and mean tumor size was 2.0 cm. Identification of IMC nodes was successful in 100 % of the cases. There were no complications. Sentinel nodes mapped to the IMC alone in 14 of 122 (11 %) patients. Overall, 26 % of patients were node positive, with 12 of 122 (10 %) patients having a positive IMC-SN. In patients with a positive axilla, IMC-SN was positive in 33 % of patients, whereas in patients with a negative axilla, IMC-SN was positive in 3 % of cases (P < 0.001). The number of positive axillary nodes was the only independent predictor of IMC positivity (1-3 positive axillary nodes odds ratio 16.9, 95 % CI 3.1-91.1; ≥4 positive axillary nodes odds ratio 45.0, 95 % CI 4.0-500.7). IMC-SN positivity led to a more advanced nodal category in all patients and more accurate staging in 4 of 12 (33 %) patients. Conclusions: IMC-SN biopsy is predictable and safe. Identification of IMC metastases though IMC-SN biopsy has the potential to alter the stage and adjuvant therapy of breast cancer patients.
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