CHANDAN CHAKRABORTY is an oncologist
with a practice in Kolkata. He specializes
in cancers of the colon and rectum.
During a conversation about his daily
endeavours, he mentioned an occupational
hazard: "My patients want to
know if they have cancer but the ordeal
of going through colonscopy is too
much for them. Imagine sticking a camera
with light bulbs into their rectum.
This allows the doctor to check the walls
of the rectum for abnormal cell growth.
It is not painful but requires the patient
to be sedated, not to mention the
amount of discomfort he or she has to
Efforts to find non-invasive cancer screening tests have been several; they have invariably failed. But this did not deter scientists from the department of Gastroenterological Surgery and Surgical Oncology at the Okayama University, Japan, who have had some luck. "We sought to develop a test by analysis of DNA methylation from cancer cells that are cast off with the faeces," said Takeshi Nagasaka, the lead author of the paper published in the August issue of the Journal of the National Cancer Institute.
Cancer cells are noted for their abnormal speeds of division and growth. Goes without saying that gene expression in these cells is abnormal too. DNA methylation is often seen in cancerous cells and used as a marker to identify them. In this a methyl group is added to the nitrogen base of DNA at two specific gene promoter regions. Promoter regions are those that promote the expression of a gene for the synthesis of proteins. If the promoter region is tampered with, gene expression also turns abnormal.
In cancer patients, some cells are sloughed off from the gastrointestinal tract, so small amounts of DNA from these cells are present in stool samples. 788 gastric and rectal tissue specimens were analyzed to see if methylation of the gene promoter regions could be used as an indicator of the disease.
The team then obtained 296 faecal samples from patients suffering from gastric and colorectal cancers as well as normal people. The researchers successfully identified methylated DNA in the faeces of 57.1 per cent gastric cancer patients, 75 per cent colorectal cancer patients and about 11 per cent of people without any active diseases.
The method seems promising. Once it is employed, Chakraborty might be relieved to see more relaxed faces leaving his clinic.
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