THE HPV DNA test, paired with routine Pap smears, increases the chances of detecting cervical cancer at an early stage.
The Pap smear has been used to test for cervical cancer in women for nearly a century.
While effective, the Pap test isn’t foolproof. Women who tested negative for signs of the disease, like cell changes or abnormal cells, have been found to have the cancer later, while others with positive results have been found to have no cancer upon further testing.
A new screening tool has recently become available, which when used together with the Pap smear – known as co-testing – raises the chances of detecting the cancer substantially. The two tests showed higher sensitivity in detecting smaller numbers of cancerous or abnormal cells. This means that women found to be at low risk of the cancer no longer need to be tested as often as with the Pap smear alone.
“It is important to detect the disease accurately in the first round of tests so that treatment can be started. If the first test misses signs of the disease, it may be another three years before the next test is taken. Some women may have developed cancer by then,” said Professor Tay Sun Kuie, Senior Consultant, Department of Obstetrics and Gynaecology, Singapore General Hospital (SGH).
Cervical cancer is highly preventable and curable. Indeed, since the Pap smear started becoming more widely available in Singapore in the last few decades, cervical cancer incidence has dropped dramatically. It is no longer the top most common cancer among women nor the commonest cancer killer as early signs of the disease, such as abnormal or precancerous cells, are quickly treated to prevent the cancer from developing or spreading.
Nearly all cervical cancer cases are caused by the human papilloma virus or HPV. But just 14 of the more than 120 strains of the virus are associated with pre-cervical or cervical cancer. And of this number, the two most common and aggressive types are HPV 16 and 18. Together, they are responsible for about 70 per cent of cervical cancer cases.
The new tool, an HPV DNA test, is able to detect the presence of all 14 HPV strains and to single out HPV 16 and HPV 18. Also, it is able to pick out the presence of squamous cell carcinoma, a common cancer which has a premalignant phase. The test is also able to detect adenocarcinoma of the cervix, an aggressive cancer that is on the rise and which often strikes younger women, much earlier than the Pap smear. Unlike squamous cell carcinoma, adenocarcinoma doesn’t have a warning stage, making early identification crucial.
HPV is the most common sexually transmitted infection worldwide, but most infections are harmless and will clear on their own within months. In this regard, women who test negative with both the Pap smear and HPV DNA test need not be tested again for the next five years. A Pap smear test is recommended every three years; high-risk individuals are encouraged to get tested more often. “Our primary interest in using the HPV DNA test is not to detect whether a woman has HPV but to correlate HPV to the presence of a pre-cancer,” Prof Tay said. SGH began offering co-testing in November 2013 for women above 25 years old.
So far, around half of the 10,000 women screened at SGH for cervical cancer have opted for co-testing. According to the hospital’s data of 1,900 women who underwent both tests between November 2013 and August 2014, almost 100 per cent of cervical cases were picked up, versus the 70 per cent that would have been if just the Pap smear was done.
• This story was first published in Singapore Health, Mar-Apr 2017 issue.