EGF and cancer: Our observation of reduced EGFR sulfenylation in response to EGF in various cancer cells (A549, H187), in spite of increased EGFR kinase activation, appears to be at odds with previous studies by Truong and coworkers who demonstrated that brief EGF stimulation (2 min) of A549 cells also enhanced EGFR sulfenylation26, whereas our results indicated a loss of sulfenylated EGFR as early as 5 min after EGF stimulation.