Targeted treatments like Iressa and Tarceva, take advantage of the biologic differences between cancer cells and healthy cells by "targeting" faulty genes or proteins that contribute to the growth and development of cancer. Many times these drugs are combined with chemotherapy, biologic therapy (immunotherapy), or other targeted treatments.

Clinicians consider the biology of the tumor cell along with the site of the tumor when determining treatment. They are learning that the same enzymes and pathways are involved in many types of cancer. However, understanding targeted treatments begins with understanding the cancer cell. In order for cells to grow, divide, or die, they send and receive chemical messages. These messages are transmitted along specific pathways that involve various genes and proteins in a cell.

Targeted treatments fight cancer by correcting or modifying defective pathways in a cancer cell. In healthy cells, each pathway is tightly controlled. In cancerous cells, certain points in the pathway become disrupted, usually through a genetic mutation (change in form).

Serious consequences to the cell may result from these mutations, depending on which pathway is affected. For example, suppose a cell develops a mutation that causes it to continue dividing into new cells? In other words, the signal is always on. If the signal never turns off, the cells that keep growing may eventually form a tumor.

Because many cancer cells use similar pathways, the same drug could be used to treat one person's breast cancer and another person's lung cancer, as long as each tumor contained similar targets. This is why many of these treatments are being used in a variety of cancer types.

There is a challenge though, to identify which patients the targeted treatment will be effective. Initially, when Iressa or Tarceva was used in patients with lung cancer, researchers discovered that only patients whose tumors contained specific mutations responded to the drug. This new research data may confirm that this is not necessarily true. Patients across a broad range of clinical characteristics could benefit.

The introduction of targeted drugs has not been accompanied by specific predictive tests allowing for a rational and economical use of these drugs. However, given the technical and conceptual advantages of cell-based functional analysis, together with its performance and the modest efficacy of therapy prediction on analysis of genome expression, there is reason for a renewal in the interest of Oncologic In Vitro Chemoresponse Assays for optimized use of medical treatment of malignant disease.