Mapping of the functional anatomy of lymphatic drainage to the axilla in early breast cancer: A cohort study of 933 cases.

INTRODUCTION: The aims of this study were to investigate the correlation between lymphatic drainage and the sentinel lymph node (SLN) status of the subregions in the context of the clinic-pathological parameters of the tumour and the coverage of the axillary volumes by standard and high tangential fields (STgF and HTgF) for whole breast radiotherapy and axillary reverse mapping (ARM).

PATIENTS AND METHODS: 933 women with early breast cancer and clinically negative axillary status underwent breast surgery and SLN biopsy followed by axillary lymph node dissection in SLN-positive cases. The subregional localisation of the SLN(s) was registered and statistically analysed with the clinic-pathological characteristics of the breast tumour. In node-positive patients treated with breast-conserving therapy in whom the SLNs were found in the anterior or posterior axillary subregions, the axillary volumes were contoured using the Radiation Therapy Oncology Group contouring atlas (n = 61).

RESULTS: In 91.1% (n = 797) of the cases, the SLN appeared in the anterior, posterior or central subregions. Using HTgF, Level I or II were completely covered in 65.6% (40/61) and 6.6% (4/61) of the cases, respectively. With STgF, the complete coverage was 0% for both levels. 6.8% (n = 63) of all cases had one positive lymph node in the expected ARM lymph node regions.

DISCUSSION: A SLN is more than likely to be present in the anterior, posterior and central axillary subregions. Tangential fields allow only limited coverage of the axillary volumes. Preserving the lateral subregion during ARM may increase the possibility of understaging.