Incidence of internal mammary node metastases after a sentinel lymph node technique in breast cancer and its implication in the radiotherapy plan

Abstract

Purpose: To analyze the frequency in determining pathologically proven metastatic involvement of internal mammary nodes (IMN) after sentinel lymph node (SLN) technique in breast cancer and to evaluate the implications for radiotherapy (RT) management of patients.

Methods and materials: Two hundred and twenty-five patients who underwent lymphatic mapping for early breast cancer treated with breast-conserving surgery and radiation (80%) or mastectomy (20%) were evaluated. There were two phases in the study: the validation phase (105 patients, 52 T1, 53 T2 < or = 4 cm), and the application phase (120 patients, 70 T1, 50 T2 < or = 2.5 cm). In the validation, if a drainage pathway to the IMN was identified, no biopsy was performed in this phase. In the application, if the study showed metastases in the IMNs, biopsy was performed. When histologically proven IMN metastases were detected, RT was included on the IMN chain planned with a 3D treatment system using conformal techniques. At the beginning of the study the injection site was subdermal and subsequently, the injection site was changed to peritumoral and intratumoral to search for IMN.

Results: In 31 patients of 225 (14%) hot spots were observed in the internal mammary chain (11.5% and 17.2% in the validation and application phases, respectively). In the validation phase, in 11 cases (11.5%) IMN drainage was observed, and in the application phase, in 20 cases (17.2%). Sampling of the internal mammary basin based on lymphoscintigraphy results was successful in 69% of the cases (14 of 20) and revealed metastatic involvement in 14% (2 of 14). This represents incidence of only 1.7% (2 of 116) in early breast cancer patients with SLN study in the application phase. In both cases the axillary SLN was also positive. Both patients with metastatic involvement of the IMN area received RT on the IMN chain next to the remaining breast after conservative surgery.

Conclusions: We can conclude that 14% of the patients with intraoperative drainage into the IMN surgical examination of the lymph nodes had pathologically positive metastases. The percentage in pathologically proven metastatic involvement of IMN after the SLN technique in early breast cancer is low, but it is not negligible. Moreover, it is expected to increase since the international recommendations have established a 3-cm cutoff for practicing the SLN technique. Although the real value of IMN irradiation in early breast cancer is not known, including this chain in postoperative radiotherapy is not recommended unless pathologically proven IMNs have been produced by the SLN technique. To avoid overdosage or underdosage in the joint between the medial tangential and IMN fields, an individualized 3D dosimetry study is mandatory to enhance dose distribution and reduce the heart volume to lessen side effects.