cervical screening

Cervical screening is the process of detecting and removing abnormal tissue or cells in the cervix before cervical cancer develops. By aiming to detect and treat cervical neoplasia early on, cervical screening aims at secondary prevention of cervical cancer. Primary prevention of cervical cancer is vaccination against HPV. Several screening methods for cervical cancer are the Pap test (also known as Pap smear or conventional cytology), liquid-based cytology, the HPV DNA testing and the visual inspection with acetic acid. Pap test and liquid-based cytology have been effective in diminishing incidence and mortality rates of cervical cancer in developed countries but not in developing countries. Prospective screening methods that can be used in low-resource areas in developing countries are the HPV DNA testing and the visual inspection. There are wide disparities in cervical screening rates and outcomes, with about 90% of deaths from cervical cancer in 2018 occurring in low and middle-income countries. To help coordinate resources to address this gap, the World Health Organization in 2020 adopted the Global Strategy for Cervical Cancer Elimination. This created the goal of vaccinating 90% of women against HPV by age 15, screening 70% of women by age 35 and again by age 45, and treating and managing 90% of patients with pre-cancer and invasive cancer, respectively.

Recommendations

Different countries have different cervical screening recommendations.
* In Europe, most countries suggest or offer screening between the ages of 25 to 64. According to the 2015 European guidelines for cervical cancer screening, routine HPV primary screening should not begin under 30 years of age. Primary testing for oncogenic HPV can be used in a population-based programme for cervical cancer screening. In England, the NHS cervical screening programme is available to women aged 25 to 64; women aged 25 to 49 receive an invitation every 3 years and women aged 50 to 64 receive an invitation every 5 years to undergo HPV testing. If there is a positive HPV test result, then patients undergo further cytology (Pap smear).
* In the United States, screening is recommended for women between ages 21–65, regardless of age at sexual initiation or other high-risk behaviors. For healthy women aged 21–29 who have never had an abnormal Pap smear, cervical cancer screening with cervical cytology (Pap smear) should occur every 3 years, regardless of HPV vaccination status. The preferred screening for women aged 30–65 is "co-testing", which includes a combination of cervical cytology screening and HPV testing, every 5 years. However, it is acceptable to screen this age group with a Pap smear alone every 3 years or with an FDA-approved primary high risk HPV test every 5 years. In women over the age of 65, screening for cervical cancer may be discontinued in the absence of abnormal screening results within the prior 10 years and no history of high-grade lesions. Management of screening results is based on recommendations by the American College of Obstetricians and Gynecologists and other professional organizations.
* In Australia, screening is offered to women aged 18–70, every two years. This is by Pap smear, and regardless of sexual history. In Canada, where screening programmes are arranged at provincial level, the general recommendation is not to begin routine screening until the age of 25 in the absence of specific reasons to, then to screen every three years until the age of 69. In Ontario, "The Ontario Cervical Screening Program recommends that women who are or have been sexually active have a Pap test every 3 years starting at age 21."
* In Thailand, the Ministry of Public Health recommends women from age 30-60 receive primary HPV testing every 5 years. Based on the results of the test, those with higher risk strains of HPV will be referred for colposcopy, while those with lower risk strains will be referred for cytology.
* In low-resource countries, decisions regarding cervical screening are made based upon available resources and thus it is often not possible to offer cervical screening as frequently. The greatest impact on cervical cancer reduction appears to result from screening women aged 30 to 39 years, so resources may be directed to that age group.

Screening process

The procedures for testing women using Pap smear, liquid-based cytology, or HPV testing are similar. A sample of cells is collected from the cervix using a spatula or small brush. The cells are then checked for any abnormalities.

To take the sample of cells, the health care clinician inserts an instrument, called a speculum, inside the vagina. The speculum has two arms that spread the walls of the vagina apart in order to see the cervix. Then, they scrape the surface of the cervix with a spatula or small brush. This collects a sample of cells from the outer layer of the cervix.

With a Pap smear, cells collected using a spatula are smeared onto a slide for examination under a microscope. In liquid-based cytology, a sample of cells is taken using a small brush. The cells are put into a container of liquid, and analysed for abnormalities. Cervical cells to be tested for HPV are collected in a similar way.

Removal of abnormal cells

Women may be told that they have CIN (cervical intraepithelial neoplasia), or CIS (carcinoma in situ) — these terms describe different levels of abnormality found in the cervical cells, with 3 classes of CIN: I, II and III in ordering of increasing stage/severity. Abnormal cells can be removed or destroyed using one of several different procedures.

Laser ablation and cryotherapy treat just the part of the cervix that contains abnormal cells. Laser ablation uses a laser to burn away the abnormal cells, while cryotherapy uses a cold probe to freeze the cells away. These procedures allow normal cells to grow back in their place. The loop electrical excision procedure (called LLETZ or 'large loop excision of the transformation zone' in the UK), cervical conization (or cone biopsy) and hysterectomy remove the whole area containing the cells that could become pre-cancerous or develop into cervical cancer.

Types of screening

There are a number of different types of screening method available. In the United States, cervical screening is usually performed using the Pap test (or 'smear test'), though the UK screening programmes changed the screening method to liquid-based cytology in 2008.

Conventional cytology

In the conventional Pap smear, the physician collecting the cells smears them on a microscope slide and applies a fixative. In general, the slide is sent to a laboratory for evaluation.

Studies of the accuracy of conventional cytology report:ACP Journal Club
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