Does the TNM classification of solitary internal mammary lymph node metastases in breast cancer still apply?

PURPOSE: TNM classification of solitary internal mammary lymph node metastases (IMLNMs) in breast cancer varies depending on their method of detection: sentinel lymph node biopsy (pN1b) or clinical examination including radiological and/or physical examination (pN2b). This study aimed to evaluate whether there is a difference in prognosis between both groups. METHODS: Data of all patients diagnosed with primary invasive epithelial breast cancer between 2005 and 2008 were obtained from the Netherlands Cancer Registry. Patients with IMLNMs were divided in groups according to their pN1b and pN2b status. The main outcome measures disease-free survival (DFS) after 5 years and overall survival (OS) after 8 years were analyzed using Kaplan–Meier survival analysis. Cox regression analysis was used to determine independent predictors for DFS and OS. RESULTS: A total of 73 patients with pN1b status and 28 patients with pN2b status were included. DFS rate was 74.1% in the pN1b group compared to 85.0% in the pN2b group (p = 0.211). Regarding OS, 20.5% (pN1b) and 25.0% (pN2b) of the patients deceased within 8 years of follow-up (p = 0.589). In multivariable cox regression analysis, nodal status was not statistically significant for DFS (HR 0.29 [95% CI 0.04–2.33], p = 0.244) or OS (HR 1.04 [95% CI 0.37–2.89], p = 0.947). CONCLUSIONS: Although the TNM classification considers pN1b and pN2b to be distinct prognostic entities, we did not observe any prognostic differences between these groups. Therefore, solitary IMLNMs may be regarded as a single category in the future and revision of TNM classification should be considered.