The medical community has recognized the importance of molecular diagnostics for several decades, and this field is especially important to cancer care. Molecular diagnostics have already improved cancer diagnosis and treatment techniques, and research is continuing.

The image above shows the many areas in which molecular diagnostics could be used. This spans the entire scope of cancer care beginning with risk assessment and moving through to surveillance after diagnosis and treatment.

Before the use of molecular diagnostics, clinicians categorized cancer cells according to their pathology, that is, according to their appearance under a microscope. Borrowing tools from two new disciplines, genomics and proteomics, molecular diagnostics categorizes cancer-using technology such as mass spectrometry and gene chips.

Molecular diagnostics analyzes how these genes and proteins are interacting inside a cell. The focus is on patterns--gene and protein activity patterns--in different types of cancerous or precancerous cells. Molecular diagnostics uncovers these sets of changes and captures this information as expression patterns. Also called "molecular signatures," these expression patterns are improving the clinicians' ability to diagnose cancer and to recommend more targeted therapies based on an individuals molecular signature.

What is the role of gene analysis in molecular diagnostics?

DNA microarrays, sometimes called "gene chips," allow researchers to see the expression of hundreds or thousands of genes at one time. A DNA microarray is a thin-sized chip with thousands of single-stranded DNA fragments corresponding to various genes of interest that have been inserted into "spots" in the microarray.

A single microarray may contain 10,000 or more spots with each spot containing pieces of DNA from a different gene. A single gene chip can even hold representative fragments from the entire human genome.

What is the role of protein analysis in molecular diagnostics?

Molecular diagnostics evaluates proteins in a cell, tissue, or organism, including the shape, function, and patterns of expression. Research seeks to identify proteins involved when normal cellular pathways support malignant growth. In cancerous tissue, some of the proteins critical for normal communication are damaged, inactive, overactive, or missing entirely. The full set of proteins disrupting cellular communications may vary from one cancer type to another, and they may also vary somewhat from one patient to another with that type of cancer.

Image courtesy of the National Cancer Institute

The discovery that there are significantly fewer genes in the human genome than initially estimated has placed more emphasis on the role of proteins, not genes, in conferring biocomplexity to an organism. Proteins are generally considered one step closer to biological function than genes and their analysis provides a more direct link making proteomics the key to understanding health and disease.

In order for proteomics to be useful in molecular diagnostics, many basic biological questions remain to be answered beginning with understanding the 'normal' protein architecture in a cell and then how and why that goes wrong in cancer.

In addition the application of proteomics to molecular diagnostics has two major hurdles to overcome.

• The first and most formidable is identification and analysis of relevant tumor markers.
• The second is developing portable, sensitive, accurate instruments that can be used in the clinic.