Septin 9 is a protein from the septin family, which is fundamental to various processes within the body’s cells. Septins are involved in the final stage of cell division, a process called cytokinesis. This specific protein has become a subject of interest in medical diagnostics, leading to new methods for health screening.
The Biological Function of Septin 9
The Septin 9 protein’s primary function is to participate in cytokinesis, where the fluid-filled space of a single cell, the cytoplasm, divides to create two distinct daughter cells. During this process, septins assemble into filament-like structures that provide scaffolding. This scaffolding helps guide the separation, ensuring cell division completes successfully.
Beyond its role in cell division, Septin 9 contributes to maintaining the cell’s shape and structural integrity. The protein interacts with other septins to form supportive complexes. Different versions, or isoforms, of the Septin 9 protein are produced in various tissues, though their specific distribution is not yet fully understood.
From Protein to Cancer Marker
The transition of Septin 9 to a cancer marker involves a process called DNA methylation. Methylation is a natural chemical modification on DNA that acts like a switch, turning genes on or off without changing the DNA sequence itself. This mechanism regulates which genes are active in different cells, allowing them to perform specialized functions.
In colorectal cancer cells, the region of the SEPT9 gene that controls its activity undergoes abnormal methylation. This alteration creates what is known as methylated Septin 9 (mSEPT9), a characteristic feature of these cancer cells. This change in methylation is thought to alter the gene’s expression, which can contribute to cancer-related events like increased cell division.
As colorectal cancer cells grow and die, they release fragments of their DNA into the bloodstream. This circulating DNA contains the abnormally methylated SEPT9 gene. The presence of mSEPT9 DNA in the blood allows it to be detected through a liquid biopsy, serving as a signal for the potential presence of colorectal cancer.
The Septin 9 Blood Test for Colorectal Cancer
The Septin 9 test for colorectal cancer is a screening method requiring a simple blood draw. The test, commercially known as Epi proColon, involves collecting a blood sample from the patient’s arm. This sample is sent to a laboratory to detect the presence of methylated Septin 9 DNA, which is associated with colorectal cancer.
This screening option is designed for individuals of average risk for developing colorectal cancer and are 45 years of age or older. The test is often presented as an alternative for those who are unable or unwilling to undergo more invasive screening procedures, such as a colonoscopy.
The test is straightforward for the patient and does not require any special preparation, such as dietary restrictions or bowel prep. The convenience of a blood draw makes it an accessible option for many.
Accuracy and Limitations of Screening
A positive result from a Septin 9 test means that methylated Septin 9 DNA was detected in the blood. This indicates a higher likelihood of colorectal cancer but is not a definitive diagnosis. Following a positive result, a diagnostic colonoscopy is necessary to visually inspect the colon and confirm the presence of cancer or polyps.
Conversely, a negative result indicates that no mSEPT9 was detected. While this lowers the probability of having colorectal cancer, it does not eliminate the possibility. The test is a screening tool designed to identify individuals who may need further investigation.
The Septin 9 test has recognized limitations. Its sensitivity is lower than that of a colonoscopy, so it can fail to detect some existing cancers, resulting in a false negative. A primary limitation is that the test is not designed to detect precancerous polyps, which are abnormal growths that can develop into cancer.
A colonoscopy, in contrast, can identify and remove these polyps during the same procedure. There is also a possibility of a false positive, where the test indicates the presence of the marker, but a follow-up colonoscopy finds no cancer.