To gain mechanistic insight, we determined the effects of c-Src ablation on steady-state mRNA levels in ErbB2-driven mammary tumors using DNA microarrays, identifying 602 transcripts up-regulated and 785 down-regulated in NIC/c-SrcL/L tumors compared to NIC/c-Src+/+ controls. The gene discussed is ERBB2; the disease is breast cancer.