Further Readings

Natural History, Risk Factors and Preventive Measures for Cervical Cancer

• Cervical cancers, particularly squamous cell carcinoma and adenocarcinoma, can be classified into HPV-associated and HPV-independent types (approximately 10%).^{7, 8} In Hong Kong, 7 types of High risk HPV (i.e. HPV 16, 18, 31, 33, 45, 52 and 58) accounted for approximately 90% of cases of cervical cancer.³ Risk factors for HPV acquisition and/or persistence or cervical cancer were listed in S Table 1. It is estimated that HPV infection takes 10 to 20 years to progress to abnormal cervical cells and then to cancer.^{9, 10} Screening allows early identification of pre-cancer lesion and treatment to prevent development of cancer.
• Human papillomavirus (HPV) vaccination has been promoted as an effective strategy to prevent cervical cancer.¹¹ In individuals who were offered the 2-valent vaccine at age 12-13 years under a national vaccination programme, the corresponding estimated relative reduction in cervical cancer rates were 87% (72-94) and 97% (96-98) respectively for cervical cancer and cervical intraepithelial neoplasia (CIN3).¹¹ To align with the World Health Organization's goal of cervical cancer elimination by 2030, 9-valent HPV vaccination has been introduced for Primary 5 and Primary 6 school girls as part of the Hong Kong Childhood Immunization since 2019. However, HPV vaccination does not provide 100% protection against cervical cancer, especially HPV-independent cervical cancer.⁷ It remains essential for all sexually active women to continue practising safe sex and to refrain from smoking to prevent cervical cancer. Additionally, regular cervical cancer screening remains crucial for even vaccinated women.

Effectiveness of Cervical Cancer Screening

• The incidence and mortality of cervical cancer has been declining since the introduction of cervical cancer screening.^12-15 Compared to no screening, cervical cancer screening every three years using conventional cytology or liquid-based cytology for women aged 25 to 65 could lead to a 90-92% reduction in the cumulative incidence of cervical cancer, with cost-effectiveness ratios of $9,000 and $12,300 per year of life saved (US/YLS), respectively.^16-18 Screening every one to two years offered minimal additional protection compared to screening every three years after two consecutive normal results.¹⁹
• Cervical cancer screening is not recommended for women under 20 due to the low prevalence of cervical cancer.²⁰ For women under 25, screening should only be considered if there is a high-risk profile.³ Routine cervical cancer screening in this age group is generally not recommended because of the high prevalence of HPV infection and cytological abnormalities, which often have a chance of spontaneous regression and pose a risk of unnecessary interventions.^{21, 22} On the other hand, screening beyond age 65 was found to be not cost-effective.²³
• HPV testing was introduced to detect high-risk HPV infections and to facilitate earlier detection of cervical precancerous lesions compared to cytology.²⁴ The performance, advantages and limitations of HPV testing compared to cytology were presented in S Table 2. Women who tested negative for high-risk HPV were found to have lower cumulative risk of CIN2+/CIN3+ lesion for at least 5 years.^25-27 HPV co-testing (i.e., both HPV testing and cytology) was associated with a 40% lower risk of cervical cancer compared to cytology alone.²⁸
• In Hong Kong, the HPV vaccination program for female adolescents aged 11-12 was implemented in 2019. As the majority of the population has not yet benefited from the vaccination coverage, cost-effectiveness studies indicate that all guideline-based screening strategies utilizing HPV tests are considered cost-effective. Among these strategies, cytology combined with reflex HPV test emerges as the optimal approach for reducing cervical cancer deaths, particularly at a willingness-to-pay threshold of one gross domestic product per capita (US$47,792).²⁹