Platinum based cytostatics have been used in many solid tumors including lung and ovary over thirty years.They interact with DNA and form interchain crosslinks which starts a process that eventually leads to cell death.The usual repair mechanism for this crosslink is via nucleotide excision repair pathway.Many pathways have been identified with in vitro cancer cell line studies to use them as a chemosensitivity biomarker.Excision repair cross complementationl is a marker for DNA repair.Several years ago presenee of this biomarker has been identified as predictor of platinum resistance in non-small cell lung cancer.This finding has paved way for using modalities other than platinum compounds in this subset of patients.