Colorectal Cancer Screening: Utility of Septin-9 Assays
While colonoscopy is considered the gold standard screening method for CRC, it can be burdensome to patients; blood tests, while less burdensome, are not necessarily as sensitive.
Colorectal cancer (CRC) is the second and third most frequently diagnosed cancer in females and males, respectively, worldwide.1 In the United States alone, just under 150,000 new cases of CRC are diagnosed per year.2 Although mortality rates have declined for CRC in the United States, it still accounts for about 8.3% of cancer-related deaths.
There are multiple guidelines for colon cancer screening. While colonoscopy is typically considered the gold standard, and is a minimally invasive procedure, it can present several challenges to a patient.
The patient's preparation for colonoscopy includes the intake of clear liquids the day before the procedure and a bowel preparation that can be difficult to tolerate from a volume and taste standpoint. Most patients will have to take at least a partial day off of work and require someone to escort them home after the procedure. There is also a risk involved with the administration of anesthesia, which, although typically low, can become significantly higher if a patient is older and has several co-morbidities.
Because of the challenges associated with colonoscopy and a recent emphasis on reaching an overall 80% screening rate of the US population by 2018, health care providers should be aware of the other potential CRC screening options.
One option gaining increased interest is blood tests aimed at detecting CRC; one such blood test is for methylated septin-9.3-6 SEPT9, which encodes septin-9, is a gene on chromosome 17 that is hypermethylated in CRC but not in normal colonic tissue. Once hypermethylated within CRC cells, the septin-9 protein is released into the bloodstream and can be detected via assay. Sensitivities and specificities for detecting CRC have been reported as between 52%-73% and 84%-91%, respectively. These detection rates were higher for late stage cancers.
It is important to note, however, that blood tests such as septin-9 have not shown adequate data to support their use in the routine detection of pre-cancerous lesions such as tubular adenomas. Detection rates of these advanced pre-cancerous lesions are significantly lower, with sensitivities reported between 14%-18%.