Next, we completed a gene expression profiling study identifying a key group of early ErbB2 target genes and identify PHLDA1 as a novel downstream target of ErbB2 signaling with a functional role in negative feedback mechanisms to fine-tune the output of ErbB2 signaling and thereby significantly enhancing the sensitivity of ErbB2-positive breast cancer cells to lapatinib. The gene discussed is PHLDA1; the disease is breast carcinoma.