Improved methods are provided for treating cancer patients, particularly patients suffering from lung cancer. Methods are provided for identifying whether a lung tumor will be responsive to treatment with a therapeutic regimen that includes pemetrexed and optionally includes cisplatin. A specific FR-a fragment peptide and a specific GART fragment peptide are precisely detected and quantitated by SRM-mass spectrometry directly in lung tumor cells collected from lung tumor tissue that was obtained from a cancer patient and compared to reference levels in order to determine if the lung cancer patient will positively respond to treatment with the c therapeutic regimen.
