The present invention belongs to the field of improved personalized medicine. More precisely, the present invention relates to a method for progressively optimizing the 5 -FU dose administered by continuous infusion in patients treated by a FOLFIRI regimen or a similar regimen, based on the 5 -FU plasmatic concentration measured during the previous 5 -FU continuous infusion and on a herein described decision algorithm. The present invention also relates to a method for treating a cancer patient in which the 5 -FU dose administered in continuous infusion in each FOLFIRI or similar treatment cycle is optimized using the decision algorithm according to the invention.
