Cervical Cancer Screening: Pap Smear Cytology versus HPV Testing
Cervical Cancer Screening is essential in detecting early cancerous changes and cancer cells in the cervix. Cervical cancer remains one of the leading causes of cancer death among women in the developing world. In Singapore, it is the 9th common cancer that affects female.
Transition of Health Protocol Globally
Current screening recommendation has been transitioning to including HPV test as part of the screening protocol. HPV testing has been proved to be effective in identifying women who are at high risk of abnormal cervical changes (dysplasia).
Singapore Ministry of Health (MOH) Guidelines
Current local Singapore MOH recommends females who are age 25 to 69, who are sexually active before, to undergo routine pap smear cytology tests every 3 years. Those who are 30 and above, are advised for additional HPV test every 5 years.
Women with abnormal screening test results are referred further for colposcopy for further evaluation.
What is HPV virus?
HPV (Human Papilloma Virus) is the major culprit of cervical cancer in females. There are over 150 strains of HPV virus. While most strains are harmless, there are high-risk HPV strains that increase women’s risks of developing cervical cancer. Having said that, not every woman infected with high-risk HPV will develop cervical cancer. HPV infection can clear up spontaneously over time in some women, while others don’t.
HPV virus is transmitted via close skin contact, typically through sexual contact. An infected person is usually asymptomatic.
What is HPV testing?
HPV test is a cervical swab test to screen for high-risk HPV strains. There are few ways of testing for HPV. HPV test can be done:
- As a co-test together with conventional pap smear cytology
- As a reflex test where HPV test is added on following an abnormal pap smear cytology
- As a sole primary HPV screening test
- HPV genotyping
HPV test becomes positive if any one or more of a set of high-risk HPV strains are detected.
HPV testing is not recommended to women age 21-29 years. This is in view of 20-30% of the women in this category can be positive for HPV infection in view of new-onset of sexual activity. The clinical significance of HPV infection in these female leading to cervical cancer is extremely rare as most women from this age group are able to clear off HPV infection by their own immune system.
Is HPV testing more sensitive than Pap Smear Cytology?
Medical research has shown HPV testing alone is able to identify more women who are later diagnosed with early-precancerous changes and cervical cancer, in comparison to just pap smear cytology alone.
Studies have shown HPV test becomes positive before cervical cancer diagnosis in 76.7% of cases, in comparison to just 59.1% of pap smear cytology samples. This shows the sensitivity of HPV testing in picking up cervical cancer. Importantly, studies also showed only 3.5% of precancerous changes and 5.9% of cervical cancer was HPV test negative yet pap smear cytology positive.
HPV test results were more likely to be positive in comparison to pap smear cytology testing in the year before the diagnosis of cervical cancer. This has led to health care policies in various counties of the world to shift the cervical cancer screening strategy to include HPV testing.
Which test(s) should I opt for?
It is estimated 5% of untreated CIN2 findings can potentially progress to invasive cervical cancer.
**CIN2 stands for cervical intraepithelial neoplasia grade 2. It is not cervical cancer, rather an early stage of cervical abnormal moderate changes that may potential leads to cervical cancer.
**Sensitivity of a test means the ability of a test to correctly pick up a disease.
Sensitivity of tests to detect CIN2
Pap Smear Cytology
Co-test with Cytology and HPV test
The key question here is which test(s) should I opt for? The statistics of efficacy has been discussed, the other consideration is really the cost effectiveness of the tests. Doing co-test is ideal, however it is much more expensive, what is the long term economic health burden? Is HPV test alone a good enough screening modalities? Do we still need to do pap smear cytology? Without co-test with pap smear cytology, there is a small risk of missing pre-cancerous and cancer cells which are HPV test negative.
HPV testing has proven to be an effective screening tool to detect early pre-cancerous changes of the cervix. It is advisable for women who are undergoing cervical cancer screening with pap smear cytology to receive repeat testing every 3 years. In additional it is recommended to co-test with HPV test every 5 years.
Speak to your doctor to understand further on pap smear, HPV testing and cervical cancer vaccination.
Aware, Screen, and Protect yourself against cervical cancer.