Region of Treatment in Radiotherapy and Second Malignancies in Breast Cancer Patients

A cohort study was conducted based on clinical records for 5248 women treated for breast cancer in Florence (Italy), with continuous follow up from 1965 to 1994. The subjects were categorised into groups such as no radiation treatment; breast dose only; and radiation doses in one, two, three or four of the following fields: namely internal mammary chain, supraclavicular nodes, axillary lymph nodes and chest wall. The Cox proportional hazards model for ungrouped survival data was used to estimate the relative risk for second cancer after radiotherapy delivered to different regions. The relative risk for all second cancers combined was statistically significantly raised if the internal mammary chain and supraclavicular nodes were irradiated. However, we found that the relative risk of the second malignancies could be reduced if all the locoregional lymph nodes (the internal mammary chain, supraclacicular nodes, axillary nodes) and chest wall are irradiated at the same time. If this finding can be verified by other large cohort studies or randomized clinical trials, it may have implications in clinical practice when deciding upon the targeted areas for radiotherapy; partial radiation treatment of the locoregional lymph nodes could raise the risk of second malignancies and should ideally be avoided.