A brief in a running series from 2013 ASCO® conference:
Prognostic Tests – to use or not use . . . or rather … To treat or not to treat?
New studies for stage II colon cancer patients contemplating chemotherapy .
by: Nancy Roach
One of the toughest decisions for patients with stage II colon cancer is whether or not to receive chemotherapy after surgery.
In a perfect world, there would be a test that could predict whether or not the cancer will reoccur and research to predict which treatment will help each patient at risk. For now, each patient’s decision is based on a wide variety of factors.
Tests to determine if the cancer has spread
Fight Colorectal Cancer hosted a webinar in 2010 with Dr. John Marshall from Lombardi Cancer Center and the late Kate Murphy from Fight Colorectal Cancer. The webinar laid out a decision-making roadmap, including a discussion of OncoType DX®, a test that may help predict risk of recurrence. Another webinar in 2011 featured Dr. Edith Mitchell from Kimmel Cancer Center and discussed research results from two similar tests, PrevistageTM and Coloprint®.
At this year’s ASCO® meeting, a poster (abstract 3639) presented by Dr. Daniel Sargent from Mayo Clinic provided an update on research around PrevistageTM . GCC is a gene present on the surface of colon cells, but not on the surface of normal lymph node cells. The PrevistageTM test looks for GCC genes in lymph node cells.
The theory is that if the GCC gene is present in lymph nodes, cells from the colon traveled outside of the colon. This type of cellular activity happens in cancer cells – not normal cells. Check out this video to learn more (note: the video was created by DiagnoCure, the company that owns PrevistageTM ).
Testing for GCC genes
Dr. Sargent’s team looked at GCC test results from lymph nodes collected between 1999 and 2008 from 463 patients with stage II colon cancer. The patients were classified as “High Risk” or “Low Risk” based on the ratio of lymph nodes with positive GCC results to lymph nodes with negative results.
Their prediction was that patients classified as “High Risk” would be much more likely to have recurrences.
The first analysis of the data did not provide the insight researchers hoped for: The GCC results classified 195 patients as “High Risk,” but only 22 of those patients had recurrences.
The team looked back to see if they could understand why their prediction was so far off and found that:
- One research site had collected lymph nodes in a way that meant the PrevistageTM test wouldn’t work correctly
- A different “risk scale” of High, Medium and Low might be more helpful
When they re-ran the data leaving out the un-analyzable nodes and the High, Medium and Low risk scale, the test results were more meaningful:
|Risk Category||# Patients||# Recurrences|
The results of the second test look more promising; however, they need to be validated with a pre-specified hypothesis.
In addition, 23 patients with Medium or Low Risk tumors also had a recurrence, which means that while GCC may be important, it is not the only factor involved with recurrence.
While PrevistageTM can’t predict whether chemotherapy will reduce the chance that cancer will come back, it may help patients and their doctors decide whether or not to undergo chemotherapy in combination with other factors.
If you are diagnosed with stage II colon cancer, there is no single test that will tell you how likely you are to have a recurrence. You and your doctor need to discuss a variety of risk factors such as:
- Micro-satellite instability status
- Depth of tumor penetration into your colon wall
- How far the tumor has penetrated your colon wall
- Risks of chemotherapy
Disclosure: Fight Colorectal Cancer has accepted funding for projects and educational programs from Genomic Health in the form of unrestricted educational grants. Fight Colorectal Cancer has ultimate authority over website content.