Impact of pathologic diagnosis of internal mammary lymph node metastasis in clinical N2b and N3b breast cancer patients

To analyze the prognostic role of pathologic confirmation of internal mammary lymph nodes (IMNs) for breast cancer patients who received neoadjuvant chemotherapy. Of the patients who were treated with neoadjuvant chemotherapy, surgery, and radiation therapy between 2009 and 2013, 114 women had suspicious IMNs and FNAB was attempted. Clinical IMN metastasis was diagnosed by 18F-FDG PET/CT positivity or pathologic confirmation (N = 70). Patients were divided into the FNAB(+) or FNAB(−) IMN group. The pathologic confirmation rate was 57% (40 of 70 patients). Rates were 74% in US-positive, 70% in MRI-positive, and 55% in PET-positive patients. Nodal stage was cN2b (6%) or cN3b (94%). Five-year progression-free survival (PFS) was significantly worse in patients with FNAB(+) IMN metastasis than FNAB(−) IMN metastasis (61% vs. 87%, P = 0.03). FNAB(+) IMN patients showed worse distant metastasis and regional recurrence-free survival without statistical significance (69% vs. 86%, P = 0.06, and 81% vs. 96%, P = 0.06). With median follow-up of 50.5 months (13.0–97.0 months), overall survival at 5 years was 77%, and PFS was 72%. Patients with FNAB-proven IMN metastasis had worse treatment outcomes compared to patients with clinically diagnosed IMN metastasis in cN2b/N3b breast cancer.