Biology Reference
In-Depth Information
types. More recently, cancers have been characterized by the level of
expression of particular genes. It has become apparent that the best way
to distinguish many different kinds of cancer is by examining their
patterns of gene expression. Knowing these patterns would allow an
accurate diagnosis and an immediate selection of appropriate therapies,
as well as facilitating the development of better treatments.
The power of microarray technology can be seen in the case of diffuse
large B-cell lymphoma (DLBCL).
1
In the United States alone, more than
20,000 people are diagnosed with DLBCL each year. The disease
progresses rapidly, and although many people diagnosed with DLBCL
were treated successfully, more than half of the patients were not.
Microscopic examination of cells from the disease revealed no basis for
predicting which cases would result in a successful outcome and which
would not. In 2000, Alizadeh et al. reported on a microarray-based
experiment that distinguished, on the basis of gene expression patterns,
two different types of DLBCL (Alizadeh et al. [2000]). One type, which
they called ''germinal center B-like DLBCL,'' was associated with much
better long-term survival rates than the other type, which they called
''activated B-like DLBCL.'' Further studies identified additional gene
expression profiles and allowed even better discrimination among
DLBCL types. The ability to accurately diagnose DLBCL has led to more
accurate prognoses and the opportunity for improved selection among
the available therapeutic options. More importantly, knowledge of the
gene expression profiles of DLBCL will allow the development of
targeted treatments, some of which are already in clinical trials (see, for
example, Abramson and Shipp [2005]).
The use of microarrays in the last decade has provided the opportunity
to compare expression patterns among thousands of different genes
under different conditions and to determine those with similar
expression patterns. When two or more genes have similar expression
profiles, they may be regulated by the same factors (co-regulated) and
may be functionally related. Identifying such groups of genes provides
clusters that warrant further detailed examination with regard to their
expression control mechanisms.
Another potential use of microarray technology is the study of cancer
chronotherapy, an approach that takes into account the fact that some
cancer therapies work better when administered at certain times of the
day than at others (see Mormont and Levi [2003]). Comparing the
circadian patterns of cancer cell gene expression with such clinical
observations should allow identification of genes that are important to
the success or failure of the treatment. Characterization of these genes
should allow better understanding of these timing phenomena, which
1. DLBCL is a common form of non-Hodgkin's lymphoma. Lymphomas are
cancers arising from lymphocytes, the cells of the immune system.
