EGFR and neoplasm: All three tumor lines had intense IHC staining that received a pathologist score of 3 + with strong, continuous membranous staining but were found to have nearly 2-orders of magnitude difference in EGFR expression determined by flow cytometry (1.2 (± 0.3) × 106, 1.6 (± 0.6) × 105, and 7.4 (± 0.4) × 104 EGFR receptors/cell in A431, Detroit 562, and FaDu, respectively; see Supplemental Table S1 and Fig S7).