Understanding the Results of the Previstage™ GCC Test
When your doctor orders the Previstage GCC Colorectal Cancer Staging Test, he/she wants to find out if you have colorectal cancer metastases in the lymph nodes removed during your surgery. The presence or absence of colorectal cancer cells in your lymph nodes gives an indication of your risk of experiencing a recurrence of your cancer, since people who have colorectal cancer cells in their lymph nodes have an overall higher risk of recurrence than those who don’t. This relationship is factored into the current system for determining the stage of your cancer. (See Understanding Staging for more details about lymph nodes and their role in determining your prognosis.)
Previstage GCC uses state-of-the-art genomic technologies to identify cancer cells in your lymph nodes that have been missed by the initial microscopic examination. During the initial microscopic test, a pathologist looks at the shape of cells in a thin slide of each lymph node, which represents only about 1% of the lymph node mass. In addition, the detection capacity is limited by the microscope. The microscope can detect one cancer cell in 200 normal cells, while genomic technologies can detect one cancer cell in 10 million normal cells. Moreover, with Previstage GCC, at least half of each lymph node is examined for the presence or absence of the GCC biomarker. (GCC is normally only found in the cells lining the intestine, so it is an excellent predictor of the spread of cancer cells when it is found in the lymph nodes, where it would not normally be found.)
Results Interpretation
Your patient report will indicate how many of your lymph nodes tested are GCC positive, GCC negative or uninterpretable as well as the ratio of positive to tested lymph nodes.
GCC positive lymph node: When a lymph node is called “positive,” it means that the GCC marker was detected, indicating the presence of colorectal cancer cells in the lymph node. In developing the test, the level of GCC required to call a lymph node positive was correlated with the level of GCC found in stage III lymph nodes (in other words, lymph nodes positive for cancer metastasis by the traditional microscopic examination method).
GCC negative lymph node: When a lymph node is “negative,” it means that the GCC marker was NOT detected, which indicates that the test did not find colorectal cancer cells in the section of the node that was tested. If all of your lymph nodes tested are GCC negative, you normally have a lower risk of recurrence. In this circumstance, your doctor may suggest that additional treatment is not necessary.
Uninterpretable lymph node: Although not common, occasionally the tissues of some of your lymph nodes have deteriorated, and it becomes impossible to process these lymph nodes to identify the presence or absence of the GCC marker. When this happens, the lymph node is called “uninterpretable.”
GCC lymph node ratio (LNR): The GCC LN ratio (LNR) is the number of GCC positive lymph nodes divided by the number of interpretable LNs. Patients with more than 10% of the interpretable lymph nodes testing as GCC positive have been shown to have a higher risk of disease recurrence than those with less than 10% of their lymph nodes testing GCC positive.
High Risk Result: A high risk stage II colon cancer patient has > 10% of their LNs positive for GCC mRNA and a 27.2% chance of disease recurrence at 5 years1, comparable to that of stage III colon cancer.2
Low Risk Result: The likelihood of disease recurrence at 5 years for a low risk patient with stage II colon cancer is 9.6%.1
Impact of T Stage and Nodes Assessed: The recurrence risk at 5 years for stage II patients with traditionally favorable prognostic factors (negative margins, T3 tumor, and > 12 LNs) was reduced to 4.0%, approaching survival outcomes observed for patients with stage I colon cancer.
The sample report available here shows you how this information gets reported to your physician, who will discuss the results with you in detail. You may also contact Signal Genetics’ Customer Care team with any questions about the test at 877-701-9007 or customerservice@signalgenetics.com.