In a recent note, I discused some theories about why the incidence of colonic cancer is increasing in younger patients (see: Why the Increased Incidence of Colonic Cancer Among Younger Americans?). Continuing in this same vein, a recent article I came across raised the issue of multigene panel testing to reveal genetic mutations in the roughly one-third of patents with early onset colonic cancer (see: Multigene Panel Testing Reveals Mutations in One-Third of Early Onset CRC Patients). Below is an excerpt from the article:
Although the overall incidence of colorectal cancer (CRC) has been decreasing in the United States over the past 15 to 20 years, the incidence of early-onset CRC has been increasing....[A]n important new study...used multigene panel testing to closely examine genetic mutations among CRC patients younger than 50. The researchers found that 16 percent of these patients did test positive for one or more genetic mutations, which might have important ramifications regarding heightened cancer risk for both the patients and their relatives.....[T]his study is the first time in which researchers used multigene panel testing to look at potentially important mutations among patients with early-onset CRC....The study of early-onset CRC patients was part of a larger study which included all CRC patients in Ohio, which is being run by the Ohio Colorectal Cancer Prevention Initiative (OCCPI). OCCPI is a statewide program involving 51 hospitals that screens newly diagnosed CRC patients and their biological relatives for Lynch syndrome, which is caused by the presence of a mismatch repair mutation in one of four genes and which heightens risk for not only CRC, but also uterine, ovarian, stomach and other cancers. Although most young CRC patients currently have their tumors screened for Lynch syndrome using tests for known changes that accompany that syndrome, the new study’s findings strongly suggest that this limited genetic testing is insufficient....The take-home clinical translation is that 16 percent of people under 50 with CRC [who undergo multigene panel testing will be found to] have something abnormal....While the cost of multigene panel testing has come down, making far more information available affordably, our current ability to interpret the results of such tests is limited. The tests often reveal a mutation or variant of unknown significance, one that is clearly not normal, but whose clinical importance (or lack thereof) is not yet fully understood.
Here's a definition for the Lynch Syndrome (see: Hereditary nonpolyposis colorectal cancer):
Lynch syndrome (HNPCC or hereditary nonpolyposis colorectal cancer) is an autosomal dominant genetic condition that has a high risk of colon cancer as well as other cancers including endometrial cancer (second most common), ovary, stomach, small intestine, hepatobiliary tract, upper urinary tract, brain, and skin. The increased risk for these cancers is due to inherited mutations that impair DNA mismatch repair. It is a type of cancer syndrome.
This information about genetic testing for patients with early-onset CRC represents one view of the beginning of a broad effort to genetically define the basis for the various cancer syndromes (see: Cancer syndrome) and asses the risk for individual patients who have one of them. This is a reasonable place to start that will eventually evolve into genetic cancer screening for the whole population. However, it's important to understand, as emphasized in the last sentence of the first quote above, that genetic testing can be fraught with difficulty. "[Genetic tests for young CRC patients] often reveal a mutation or variant of unknown significance, one that is clearly not normal, but whose clinical importance (or lack thereof) is not yet fully understood." In other words, even for patients with early onset CRC, genomic testing does not always produce an actionable, clear path forward for them or their relatives.