1. A method of using a blood biomarker to rule out the presence and calculate the probability of having carcinoma of the breast in a woman, said method comprising: blood collection in heparinized tubes and isolation of lymphocytes from women, said isolation being conducted by the Ficoll gradient technique and suspended in freezing media containing 10% dimethyl sulfoxide, 40% RPMI-1640 medium, 50% fetal bovine serum and 1% antibiotic/antimycotic, and 2.0 ml aliquots stored in −80° C. freezer, said lymphocytes being later thawed in batches for host cell reactivation assays; or alternatively, the said assay can be done with freshly collected blood that has not been frozen; measurement of the DNA repair capacity of said lymphocytes using the host-cell reactivation assay wherein a non-replicating plasmid is genetically engineered to contain a bacterial luciferase reporter gene that is not present in a mammalian cell, said gene being damaged by UV exposure in a controlled and quantitative manner, being the level of its expression a direct measure of the repair capacity of the host mammalian cell. This assay measures the total sum of the DNA repair capacity of lymphocytes, which is a reflection of the repair capacity of the donor and primarily measures DNA repair via the nucleotide excision repair pathway; calculations of DNA repair capacity wherein the standard assay for gene expression of luciferase activity is measured using a luminometer or similar instrument, the percent DNA repair capacity (DRC) being then calculated based on luminescence counts as the percentage of residual luciferase gene expression after repair of damaged plasmid DNA compared with undamaged plasmid DNA (100%); statistical methods for using DNA repair capacity to predict breast cancer risk wherein after analyzing DRC as a continuous numerical variable, DRC is divided in two levels (low and high) using the most efficient cut-off point of 3.1% to distinguish between low and high. Using this criterion DRC functions as a biomarker predictor of breast cancer with at −71.0% sensitivity and 90.2% specificity.