Incidence of internal mammary node in locally advanced breast cancer and its correlation with metastatic disease: a retrospective observational study

Objective: To determine incidence of internal mammary nodes (IMN) at baseline CT of locally advanced breast cancer (LABC) and ascertain prognostic implication. Methods and materials: Retrospective review of all LABC patients from 1 January 2012 through 31 December 2014 was performed after approval from institutional review board. CTs of 182 patients enrolled were reviewed by two radiologists independently, and IMNs were documented based on size, location and relation with location of breast primary. 3-year follow-up was analysed and incidence of metastases was calculated as overall incidence, incidence in patients with and without discernible IMN at baseline imaging. Results are presented as numbers and percentages. Differences in metastases of two groups were compared using χ2 test. 95% CI was calculated and p < 0.05 was considered significant. Results: 77 of 182 had identifiable IMN (42.3% incidence). Majority of identifiable nodes were on ipsilateral side of primary (incidence 90.90%) with higher incidence in patients with upper-outer quadrant tumours (55.9%). Majority were seen in second intercostal space (44.4%). 36 (19.7%) developed distant metastases within 3 years of therapy. Of these, 21 (27.3%) had IMN as compared with 15 (14.3 %) without IMN on baseline imaging. Patients with identifiable IMN on baseline CT had significantly higher incidence of distant metastases (p = 0.0321). Conclusion: Significant number LABC patients have identifiable IMN on baseline imaging with patients showing IMN on baseline CT showing significantly higher rate of metastatic disease following therapy. Advances in knowledge: Many LABC patients have identifiable IMNs on baseline imaging which show higher incidence of subsequent metastatic disease.