The present invention relates to methods for screening a subject for a cancer. In particular, the present invention relates to a method (A) for screening a subject for a cancer comprising the steps of i) extracting the cell free nucleic acids from a sample obtained from the subject, ii) determining the total concentration of mitochondrial cell free nucleic acids, ii) determining the total concentration of nuclear cell free nucleic acids iv) calculating the ratio of the level determined at step ii) to the concentration determined at step iii), v) comparing ratio determined at step iv) with a predetermined corresponding reference value and vi) concluding that the subject suffers from a cancer when the ratio determined at step iv) is lower than the predetermined corresponding reference value or concluding that the subject does not suffer from a cancer when the ratio determined at step iv) is higher than the predetermined corresponding reference value.