Thread by @susanmsmith

1. Cervical cancer screening is a complex area and as we move forward in Ireland we need to know the facts so that clinicians and women can make decisions about screening together in an informed way.

2. Cervical cancer is the eight commonest cancer in Ireland with 277 cases of cervical cancer per year in Ireland and 88 deaths per year in women (average age of 56 years). There are an average of 2873 cases of pre-cancer.

3. Cervical cancer is associated with HPV (Human Papilloma Virus). The first stage is the development of pre-cancerous cells (CIN). Progression from CIN to cancer takes on average 10 to 20 years. CIN is treated using Colposcopy to prevent this progression.

4. Cervical screening (CervicalCheck) is used to detect aymptomatic pre-cancer (CIN).
Substantial changes (high-grade abnormalities) = referral for colposcopy
Minor changes (low-grade abnormalities) = sample checked for HPV virus and if HPV detected, referral for colposcopy.

5. During Colposcopy, the specialist examines the cervix and may take a biopsy and/or apply treatment to the abnormal area.
Biopsy is interpreted as either normal; CIN (pre-cancer) or cervical cancer (though this is not always apparent). Further management decided in clinic.

6. No screening test is 100% accurate – can be false positives (screening tests says result is positive but there is no clinically significant disease on further testing), or false negatives (results is negative although disease is present – this may lead to delayed diagnosis)

7. What is the chance of a false negative test result?
For every 1,000 tests carried out 959 tests will be negative, 4 of these will be a false negative.

8. What is the chance of a false positive result?
For every 1,000 tests carried out, 41 will be positive requiring a repeat test or referral for Colposcopy. Of the 41 tests, 12 will be confirmed as CIN requiring treatment (true positives) Remaining 29 will be false positives.

9. Question:
If I have a normal smear test result, what is my chance of developing cervical cancer in the next three/ five years?

10. Assuming 250,000 women attend for screening each year: In women with a negative screening test, 39 will develop invasive cervical cancer within 3.5 years and 90 will go on to develop invasive cervical cancer within 5.5 years (includes true negatives and false negatives)

11. The proposed new screening strategy (not yet introduced) has fewer false negatives. So less women with a negative test will go on to develop invasive cancer (12 within 3.5 years and 22 within 5.5 years (includes true negatives and false negatives)

12. Summary information from the UK (similar to the proposed new test):
• 1 in 20 women will have an abnormal smear test result
• 1 in 2000 have cervical cancer
• So only 1% of women with an abnormal smear will have cancer

13. Key points to emphasise about cervical screening: It is not for ‘diagnosing cervical cancer’ and without screening this presents with symptoms (such as Irregular vaginal bleeding, spotting or discharge, bleeding after sex, pelvic pain).

14. It is also possible to develop cervical cancer between screening tests so women who have symptoms such as abnormal vaginal bleeding or pelvic pain should always see their GP.

15. Screening will never prevent all cervical cancer deaths. The HPV vaccine prevents cervical cancer. It prevents 7 out of 10 cervical cancers and works best when given at the age of 12 to 13 years. All international evidence indicates that the vaccine is extremely safe.