How the Previstage™ GCC Test Works
Previstage GCC is the first test to use genomic technologies to assess the stage of a colorectal cancer patient, which is known to be related to the risk of disease recurrence. The test measures the expression or absence of expression of a biomarker called Guanylyl Cyclase C (GCC or GUCY2C).
GCC as a Biomarker for Colorectal Cancer Metastasis
GCC (or GUCY2C) is the first validated marker useful in detecting the presence or absence of colorectal cancer cells in the regional lymph nodes. GCC is expressed in cells lining the intestine, and it is never found in normal tissue in other parts of the body. (The gene codes for a protein that is involved in multiple functions, including those responsible for traveler’s diarrhea.) When GCC is detected in the lymph nodes removed during a colorectal cancer surgery, it is a strong indication of the presence of colorectal cancer metastases.
More than 50 publications document the link between GCC and colorectal cancer. You can review these publications in the Publications section for physicians. Here are key highlights of the most recent findings:
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2009: Results of a prospective academic study led by Dr. Scott Waldman of Thomas Jefferson University were published in the Journal of the American Medical Association showing GCC to be the strongest independent predictor of CRC recurrence.1
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2010: A study published in the Journal of Clinical Pathology reported that patients with GCC+ lymph nodes were more than twice as likely to relapse than GCC- patients.2
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2011: A study led by Daniel Sargent, PhD, of Mayo Clinic and published in the Annals of Surgical Oncology found the group categorized as high risk by GCC testing to have a 6 times greater likelihood of recurrence than the low risk group.3
Benefits of Genomic Technologies
It is widely recognized that there is a clear link between metastases in the regional lymph nodes and the risk of disease recurrence. Currently, 1 in 5 colorectal cancer patients deemed to have lymph nodes free of metastases by microscopic examination experience a recurrence, presumably through metastases missed while examining the lymph nodes.
Microscopic examination uses a very thin slide of lymph node tissue, which typically amounts to less than 1% of the lymph node mass. The microscope can detect 1 cancer cell in a group of about 200 normal cells. With genomic technologies, such as qRT-PCR to detect the GCC mRNA expression in the lymph nodes, it is possible to overcome at least two of the weaknesses of the current microscopic method: sample size and detection sensitivity.
With Previstage GCC, at least half of each lymph node provided is examined (usually 12 nodes or more), and the technology provides a detection capacity of 1 cancer cell in up to 10 million normal cells. Overall, the genomic technologies employed in Previstage GCC are 100,000 times more sensitive than the current microscopic method and examine on average more than 375 times more lymph node tissue.
Treatment Decision
The current guidelines for colon and rectal cancer treatment recommend:
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To not treat stage I patients and most stage II colorectal cancer patients
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To consider for chemotherapy treatment stage II patients who are considered at high risk based on a number of factors
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To treat all medically fit stage III patients
A landmark study examining treatment of stage II patients found that less than 5% of stage II patients benefit from treatment.4 Considering an average of 20% of stage II patients recur, the current methods of evaluating patient risk are insufficient to accurately differentiate between patients with a high or low risk of disease recurrence as candidates for treatment. Meanwhile, several studies have concluded that patients who were GCC positive had a risk of recurrence comparable to stage III patients1,2.
There several factors that you and your doctor will take into account to decide if adjuvant chemotherapy is appropriate for you. But with regard to your risk of recurrence, Previstage GCC provides you and your doctor with the most advanced genomic information regarding the stage of your cancer.