EGFR protein expression and gene copy number in oral leukoplakia (OPL). OPL with EGFR expression scored 1+ (A), 2+ (B), and 3+ (C). Of the 49 patients considered for EGFR gene copy number, disomy (≤ 2 copies in >90% of cells) was observed in 29 (59%) OPLs (D), low trisomy (3 copies in 10 to 40% of cells) in 14 (29%) OPLs (E), high trisomy (≥ 40% of cells with 3 copies and < 10% of cells with 4 copies) in one (2%) case, low polysomy (10% to 40 % of cells with 4 copies) in 4 (8%) OPLs (F), and gene amplification (clustered unbalanced gain of EGFR) in one (2%) case.