Screening tests to detect cancer at an early stage by using expensive technology such as PET-CT (positron emission tomography-computed tomography) or magnetic resonance imaging (MRI) are useless for healthy people, a seminar was told yesterday.

Dr Vichien Srimuninnimit of Siriraj Hospital's Medical Oncology Division said the goal of cancer screening was to find pre-cancerous lesions and cancer before symptoms appear, which can help patients access treatment, but some screening tests such as colonoscopy can cause serious problems.

As well, some tests can show false-positive results, which cause patient anxiety and unnecessary invasive diagnostic procedures, which also entail risks and cost. Conversely, a false-negative result can lead to a delay in seeking medical care even if there are genuine symptoms.

"Finding cancer may not improve the person's health or help the person live longer," Vichien said.

He was speaking at the second annual "Cancer Prevention, Early Detection and Interception" conference organised by Chulabhorn Hospital, participated in by 360 cancer researchers nationwide.

"some cancers never cause symptoms or become life-threatening, but if found by a screening test, the cancer may be treated. Also, treatments for cancer have side effects," he pointed out.

Screening tests for breast, cervical, colon, prostate, lung and ovarian cancer are mostly available at private hospitals.

Citing the American Cancer Society (ACS) guideline for breast-cancer screening, Vichien said yearly mammograms should start at age 40 and continue for as long as a woman is in good health.

Clinical breast exams should be undertaken about every three years by women in their 20s and 30s and every year for woman 40 and over. meanwhile, breast self-examination is an option for women starting in their 20s.

But the US Preventive Services Task Force has recommended that mammography screening should be conducted every two years to reduce risk of breast cancer by nearly half. moreover, the USPSTF has suggested that doctors not teach women to perform breast self-examination, as it has been found to have no mortality benefit.

The ACS also recommended that asymptomatic men who have at least a 10-year life expectancy have an opportunity to make an informed decision with their healthcare provider about whether to be screened for prostate cancer, after receiving information about the uncertainties, risk and potential benefits associated with screening for that disease.

Despite the high cost and limited benefit of screening, it should be done for men with family history of prostate cancer.

However, Vichien said screening should be done for diseases that are important health problems and for which there is a detectable pre-clinical phase.

A cancer-screening method should be accepted as standard care only when its value has been demonstrated in randomised controlled trials, he said.