The NB4 APL cell lines (including the resistant ones), present detectable expression of SYK, although they are negative for EGFR, suggesting that the mechanism underlying the gefitinib-induced APL sensitization to ATRA and ATO might be linked to off-targets downstream the SYK pathway, as demonstrated previously for other AML cell lines (32). Here, EGFR is linked to acute myeloid leukemia.