Seeing into cells. The promise of in vivo molecular imaging in oncology.

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Medicine is undergoing a revolution. Disease is increasingly being redefined in terms of underlying molecular abnormalities, as opposed to the signs and symptoms of the patient. This new definition is referred to as the ‘molecular signature’ of a disease and the current developments in biomedical research are accordingly termed ‘molecular medicine’. In the case of cancer, we know that tumours result from genetic alterations of cells, which may involve overexpression or underexpression of normal genes, or mutations that generate abnormal gene products. This may affect any of the molecules within the cell, the cell membrane or the cancer‐cell milieu. In addition, the microenvironment of a tumour, including stromal and vascular endothelial cells, is important for the growth and persistence of the tumour. This entire constellation of the abnormal molecular biology of tumour cells and their microenvironment is the molecular signature of cancer (Hanahan & Weinberg, 2000). > The greatest potential value of molecular imaging is its ability to report on the molecular state of a tumour in its normal milieu One consequence of this new understanding of disease is the increased effort to develop targeted drugs that interact specifically with the altered genes or their products and either limit the progression of or kill tumour cells. The hope is that such therapeutics will selectively target tumour cells and leave normal cells untouched, thereby reducing the common side effects of current anticancer therapies such as radio‐ and chemotherapy. There is an increasing number of such targeted therapeutics being developed and made available for clinical use. For example, until about five years ago, there were few options available for treating colon cancer beyond surgically removing the affected part of the colon and using standard chemotherapy. However, since 1999, the US Food and Drug Administration (FDA) has approved at least five targeted drugs …