In oncology, the term 'targeted therapy' is used to describe drugs that target only the cancer cells and spare normal cells thereby reducing host toxicity while simultaneously increasing the eradication of cancer. Trastuzumab and imatinib are well known examples of successful targeted therapy. Newer agents like gefitinib and cetuximab offer hope that targeted therapy also may yield therapeutic benefit for such refractory malignancies as lung and colon cancers. One of many remaining challenges is to identify markers, molecular or clinical, that predict for responsiveness to a specific targeted therapy (e.g. HER2/neu positivity and trastuzumab responsiveness). However, using emerging technologies such as gene or protein profiling, it may be possible to predict a tumor's responsiveness to a particular targeted therapy based on its molecular signature. If true, clinicians might then possess the ability to predict a tumor's clinical behavior and shape its density through specific, targeted interventions.