Disclosed is a method for monitoring early treatment response of a cancer treatment comprising measuring by magnetic resonance spectroscopy (MRS), for example, proton MRS, the amount of Choline present in the cancerous tissue before and after treatment; the treatment comprises administration of a cell surface receptor inhibitor, for example, an EGFR inhibitor, whereby a decrease in the amount of Choline after treatment is indicative of a positive response. The decrease in the amount of Choline represents the decrease in the internal cell membrane as a result of down regulation of the organelles and their secretory granules and their transport vesicles. Disclosed also is a method for determining effectiveness of a cell surface receptor inhibitor in the treatment of cancer.