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
go through."
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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