Why do we need irradiation of internal mammary lymph nodes in patients with breast cancer: Analysis of lymph flow and radiotherapy studies

Aim Using clinical data and results of lymphoscintigraphy to calculate probability of internal mammary lymph node (IMLN) invasion by breast cancer (BC). To evaluate clinical value of lymphoscintigraphy as the guide for irradiation of IMLN. Methods Using the data of eight published studies that analyzed lymph flow from primary BC (4541pts) after intra-peri-tumoral injection of nanosized 99mTc-colloids we determined probability of lymph-flow from internal-central and external BC to IMLN. In 7 studies (4359pts) axillary staging was accompanied by IMLN biopsy (911pts) that helped us to estimate probability of IMLN metastatic invasion in relation to the status of axillary LN. Finally, we estimated probability of IMLN invasion by BC in five randomized and observation studies that analyzed effect of IMLN irradiation on overall survival (OS). We calculated possible gain in survival if they would be treated according to lymph-flow guided radiotherapy to IMLN. Results Lymph-flow from internal/central BC to IMLN was mentioned in 35% from external lesions – in 16% cases. In women with negative axillary LN metastases in IMLN were revealed in 7.8%pts, in the case of positive axillary nodes average risk of IMLN invasion increased to 38.1%. Calculated probability of IMLN metastatic invasion in pts included in evaluated trials did not exceed 10%. If lymphoscintigraphy would drive decision about irradiation of IMLN than 72–78% of pts included in these studies would escape radiotherapy to IMLN. In the remaining 21–28%pts with lymph-flow to IMLN their irradiation probably would increase gain in OS from 1.0–3.3% to 4.3–16.8%. Conclusion Lymphoscintigraphy can be used to optimize the strategy of IMLN irradiation.