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Development of Novel Immunotherapeutics 165<br />

Figure 10 The diversity of biomarkers and their usefulness.<br />

that started to relapse or progress after standard therapy, while the process is not<br />

clinically evident yet (e.g., PSA- or CA-125-positive patients with no overt<br />

clinical disease). The reason is that cancer vaccines are more applicable to<br />

indications associated with limited disease burden or minimal residual disease;<br />

therefore, identifying patients in that earlier stage is of paramount importance. In<br />

addition, since the length of clinical trials is a limiting factor in the development<br />

of therapies for oncologic disorders, in a setting of limited disease, biomarkers<br />

that correlate and anticipate clinical progression are critical in providing timely<br />

data set that would support a rationale for a decisional process. Finally, patient<br />

stratification approaches based on biomarkers and applied to minimum residual<br />

disease post-standard therapy may result in identification and expedited evaluation<br />

of efficacy of investigational agents. There are quite several markers in this<br />

expanding category such as VEGF, CA-125, and PSA. If validated through<br />

clinical experimentation, such biomarkers—alone or as clusters—may become<br />

important diagnostics complementary to more conventional approaches. With<br />

the emerging maturation of various databases on biomarker expression in human<br />

normal tissues as well as diseased tissues or tumor archives resulting from<br />

worldwide omics efforts, there is an exciting possibility for target discovery<br />

based on biomarker database mining. Careful computer-based analysis of proteomics,<br />

transcriptomics, and genomics data may reveal entire signal transduction<br />

pathways with associated membrane receptors amenable to biomolecule<br />

targeting and downstream enzymes that can be targeted via conventional small<br />

molecule technologies.<br />

A category of biomarkers of paramount importance for the development of<br />

new molecular targeted therapies is that of markers that predict responsiveness to<br />

an investigational drug. Since molecular pathogenesis and thus tumor susceptibility<br />

to drugs is quite heterogeneous, these biomarkers have a severalfold<br />

impact: First, they would outline a subpopulation of patients that would benefit<br />

the most from drug exposure; second, that would minimize unnecessary exposure<br />

of patients that are less likely to benefit from the drug. Overall, this would<br />

lead to more rapid, focused development of the drug by increasing therapeutic

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