The present invention is related to an in vitro method for identifying deficient BRCA1 function in a test biological sample obtained from a human individual, said method comprising the steps of: - Assaying the test sample to determine an expression profile of at least BRCA1 gene and ID4 gene; and - Establishing the ratio of BRCA1 to ID4 gene expression; Wherein a BRCA1/ID4 ratio lower than a threshold value is used as positive criterion for identification of the deficient BRCA1 function in the tested sample.
