Faecal detection of cancer

CHANDAN CHAKRABORTY is an oncologistwith a practice in Kolkata. He specializesin cancers of the colon and rectum.During a conversation about his dailyendeavours, he mentioned an occupationalhazard: "My patients want toknow if they have cancer but the ordealof going through colonscopy is toomuch for them. Imagine sticking a camerawith light bulbs into their rectum.This allows the doctor to check the wallsof the rectum for abnormal cell growth.It is not painful but requires the patientto be sedated, not to mention theamount of discomfort he or she has togo through."

Efforts to find non-invasive cancerscreening tests have been several; theyhave invariably failed. But this didnot deter scientists from the departmentof Gastroenterological Surgery andSurgical Oncology at the OkayamaUniversity, Japan, who have had someluck. "We sought to develop a test byanalysis of DNA methylation from cancercells that are cast off with the faeces,"said Takeshi Nagasaka, the lead authorof the paper published in the Augustissue of the Journal of the NationalCancer Institute.

Cancer cells are noted for theirabnormal speeds of divisionand growth. Goes withoutsaying that gene expressionin these cells isabnormal too. DNAmethylation is oftenseen in cancerous cellsand used as a marker to identify them.In this a methyl group is added to thenitrogen base of DNA at two specific genepromoter regions. Promoter regions arethose that promote the expression of agene for the synthesis of proteins. If thepromoter region is tampered with, geneexpression also turns abnormal.

In cancer patients, some cells aresloughed off from the gastrointestinaltract, so small amounts of DNA fromthese cells are present in stool samples.788 gastric and rectal tissue specimenswere analyzed to see if methylation ofthe gene promoter regions could beused as an indicator of the disease.

The team then obtained 296 faecalsamples from patients sufferingfrom gastric and colorectal cancersas well as normal people.The researchers successfullyidentified methylated DNA inthe faeces of 57.1 per cent gastriccancer patients, 75 per centcolorectal cancer patients and about 11per cent of people without any activediseases.

The method seems promising. Onceit is employed, Chakraborty might berelieved to see more relaxed faces leavinghis clinic.