GINA MENZIES – If uptake of cancer screening declines, then the crisis will have become a total tragedy
THE recent controversy and media discussions surrounding cervical screening by a smear test have blurred the differences between screening and diagnosis. This has created confusion for many people who now may consider it not worth their while taking up the invitation for free screening.
Repeatedly, commentators refer to screening as if it were diagnosis. Rather it is a tool to examine healthy populations to see if there is any pre-clinical abnormality that might need further analysis. Screening whole populations is not intended to diagnose conditions.
It tests for a condition on healthy people who do not show any symptom of the condition. In the case of cervical smears, screening looks at human cells.
Examination of these may indicate the possible future development of a disease for which there is a treatment that is effective. A diagnosis to establish what is the cause of a patient’s symptoms only comes after many other tests.
The National Screening Service Programme has been implemented in Ireland over recent years. BreastCheck commenced in 2000, CervicalCheck in 2008 and bowel screening in 2012.
Breast cancer is the most common cancer in women. BreastCheck was initially introduced for all women between the ages 50 and 64. An invitation is sent every two years. Since 2015, this cohort has been extended to include women up to the age of 69.
The most recent BreastCheck report of 2015/2016 shows 1.5 million mammograms have been generated, with 500,000 women involved. The detection rate of 9.5 per 1,000 mammograms is better than the international guideline of seven per 1,000 mammograms.
Bowel cancer is the second most common cancer in Ireland. In 2012, the self-administered bowel test known as faecal immunochemical test (Fit) was launched for women and men between 60 and 69.
It is planned to invite participants every two years and to increase the test availability to all between 55 and 74. In the first phase of this screening, 521 cancers were detected, at a rate of 2.65 per 1,000.
These figures will undoubtedly grow as the test is implemented on a whole population scale.
The Pap smear test for cervical cancer is one of the few screening programmes that has achieved an almost exhaustive coverage across the world.
CervicalCheck was introduced in 2008 in Ireland and offered to women between the ages of 25 and 60. The objective of the smear test is to detect pre-cancerous cells, which may or may not subsequently become cancerous.
There may be many reasons other than cancer why cells in the cervix appear abnormal, and a more complex analysis may be required. Since 2008, more than three million smear tests have been carried out in Ireland, with over 50,000 cases of cell changes detected.
Dr Noírín Russell, lead colposcopist at University Hospital Kerry, recently stated that “if you perform 1,000 smear tests, in that 1,000 there would be 20 abnormal smears and CervicalCheck would pick up 12 of these”.
The information leaflet given to women before the test clearly indicates that cervical screening will not detect all cases of cervical cancer. Because these tests do not pick up all pre-cancerous cells, it does not mean that the test should be forgone. Nevertheless, since 2008 there has been a 7pc reduction in cervical cancer.
The HPV (human papilloma virus) vaccine now given to girls over 12 years of age can prevent seven out of 10 cervical cancers. In 2019, the National Screening Service will also screen for HPV – this test is even more efficient than CervicalCheck. Such advances in screening and vaccination are welcome developments for all women.
The descriptions “false negative” and “false positive” have entered our conversations about cervical smears. A false positive may incorrectly show a positive result for those with no abnormal cells.
When a smear test gives a positive result, a procedure called a colposcopy (a more detailed examination of the cervix) will take place, usually on an out-patient basis to follow up the screening result. It will confirm the positive result or indicate that it is a false positive.
FALSE negatives are more problematic. They are part and parcel of any screening programme. A false negative occurs when the result indicates there are no precancerous cells at the time, but such cells are found in a subsequent test or following diagnostic tests because of presenting symptoms.
The National Screening Service Programme, which also includes diabetic retina screen, is not designed to be diagnostic and will often have significant rates of false positives and false negatives. This, however, is not a reason to eschew the screening programme.
Screening does not diagnose whether a person has cancer. It only identifies changes in cells, and that may indicate that further testing is required.
Hopefully, the Scally inquiry and later ones will provide further answers to the ongoing questions and reinforce the value of cervical screening.
What is important is that the programmes continue and those invited to participate do so, at the same time knowing this will never be 100pc accurate. A 70pc take up is necessary: should this decrease because of the current controversy, that would be a national tragedy.