Personalized Medicine - page 7

3. Diagnostic Tests:

Diagnostic tests will play an ever more important role in personalized medicine. Cancer molecular diagnostics involves the measurement of DNA, RNA, proteins, or metabolites to detect a person's genetic makeup. Any changes in the DNA of a cell, or changes in chemical processes associated with it, may soon be used to determine the presence of cancer.

The term companion diagnostic means that the particular diagnostic test under evaluation is specifically linked to a known therapeutic drug. This linkage could be important in the therapeutic application and clinical outcome of a drug (personalized medicine).

		Reminder: Genomics is the study of all the genes in a cell or organism. Proteomics is the study of all the proteins made by those genes.
Image courtesy of the National Cancer Institute

While the traditional pathological examination of cancer remains an essential clinical tool, newer technologies such as microarrays, RT-PCR, mass spectrometric proteomic analyses, and protein chips are moving to center stage, although not yet routinely used by all or in all cancer types.

Well-designed, prospective clinical studies are needed to demonstrate that the diagnostic test results influence the patient's management such that clinical outcomes are improved.

However, the studies necessary to develop evidence of the value of these tests may be costly and lengthy, especially for tests used for cancer screening. This deters diagnostic companies from conducting such studies.

A few examples of diagnostic tests now in use:

• A whole-genome screen to identify those genes active in cutaneous T-cell lymphoma, CTCL cells that govern whether the cancer cells respond to the drug SAHA (Vorinostat or Zolinza) or not.
• Oncotype DX, a diagnostic test on a chip engineered to detect patterns of genetic abnormalities within tumors. These patterns are prognostic and can help guide treatment decisions. This test is available for both breast and colon cancer.

For more information on diagnostic tests go to:
https://cisncancer.org/research/new_treatments/molecular_diagnostics/index.html

4. Pharmacogenomic Testing:

Dihydropyrimidine dehydrogenase test. The medication 5-fluorouracil (5-FU) is one of the most commonly used chemotherapy medications. Some people have a genetic variation that results in a decrease in the dihydropyrimidine dehydrogenase enzyme, which is responsible for breaking down 5-FU.

		As a result of this deficiency, some people may develop severe or even fatal reactions to 5- FU.
Image Courtesy: Erasmus MC at University Medical Center Rotterdam

Knowing ahead of time who has this deficiency can help doctors tailor the medication dosage to prevent these kinds of dangerous adverse reactions.

5. Using Biomarkers

A major challenge in development of cancer biomarkers will be the integration of proteomics with genomics and metabolomics data, as well as their interpretation with clinical data and epidemiology. It is also necessary to distinguish between the various types of biomarkers:

	Disease-related biomarkers give an indication of whether there is a threat of disease (risk indicator or predictive biomarkers), if a disease already exists (diagnostic biomarker), or how such a disease may develop in an individual case (prognostic biomarker). The early stages of cancer development carry the maximum potential for successful treatment interventions. However, these stages are often asymptomatic, leading to delayed diagnosis. Biomarkers have the potential to lead the way in early diagnosis. Drug-related biomarkers indicate whether a drug will be effective in a specific patient and how the patient's body will process it.
Image provided by CISN archives. All rights reserved.

A few examples

• Prostate specific antigen (PSA): Elevated levels may suggest the presence of prostate cancer (see problems below).
• Cancer antigen 125 (CA-125): Elevated levels suggest recurrent ovarian cancer.

Unfortunately, both tests may result in:

False negatives - failure to detect cancer in those who have it (poor sensitivity), or

False positives - a positive test result for the presence of cancer in people who are actually cancer-free (poor specificity).

• Measuring for the erbB2 and EGFR proteins for selecting breast, lung and colorectal cancer patients for specific targeted therapies.

For a table with 30 protein tumor markers and where they are used, go to:
https://cisncancer.org/research/new_treatments/tumor_markers/promise_003.html

Image provided by CISN archives. All rights reserved.

Human DNA may be 99.9% similar across the population but just like Zebras, that remaining .1% allows us to each display our individual "stripe".