Radiation-induced malignant transformation of pre-neoplastic and normal breast primary epithelial cells.

Radiation is used in multiple procedures as a therapeutic and diagnostic tool. However, ionising radiation can induce mutations in the DNA of irradiated cells, which can promote tumorigenesis. As malignant transformation is a process that takes many years, there are intermediate stages of cells that have initiated the process but have not yet evolved into cancer. The study here aimed to investigate the effect of ionising radiation on normal and partially-transformed human mammary epithelial cells. Breast Primary Epithelial Cells were derived from normal breast tissue from two different donors and modified by transduction with the SV40 small and Large T antigen and hTERT genes to obtain partially-transformed cells and also with HRAS to completely and experimentally transform them. After exposure to different doses of ionising radiation, oncogenic features were analysed by means of an anchorage-independent growth assay and 3D cell culture. The addition of radiation exposure resulted in an increase in the number and size of colonies formed in each of the conditions analysed and in the reduction of the capacity of partially-transformed cells to form properly polarised 3D structures. Moreover, partially transformed cells require lower doses of radiation than healthy cells to enhance anchorage-independent growth capacity. Although cells from different donors have a different degree of sensitivity in the response to radiation, a higher sensitivity to the radiation-induced cell transformation process was observed in those cells that had already initiated the oncogenic process, which require higher doses of radiation to complete the transformation process. Implications: Individuals carrying accumulation of genetic alterations may have an increased susceptibility to radiation-induced neoplastic transformation.