Changes in the cells of the cervix occur in an area known as the transformation zone, a small piece of tissue just at the top of the vagina where those cells join the entrance to the womb.
Abnormalities in smear tests are graded according to levels of cervical intraepithelial neoplasia, or CIN1, CIN2 and CIN3. The first two of these low-grade abnormalities will, in the majority of cases, return to normal over time.
About one-third will persist and a small number will progress to the next level of abnormality. But at all stages, up to the high-level CIN3 abnormality and even in the early stages of invasive cancer, successful treatment can be given.
A very small number of cervical cancers are adenocarcinomas, or glandular cancers, and occur in the glands inside the cervix - they won't be picked up by smear tests.
While most of the low-grade abnormalities will regress, it is likely the majority of CIN3 abnormalities will progress if they are left untreated.
But the progression from an abnormality in the cervix to invasive cancer takes place over a very long timeframe in the region of 15 years, plenty of time to monitor and treat a potential problem.
If abnormalities persist, a woman may be sent for a procedure known as a colposcopy. This involves examination of the cervix using a special microscope. The gynaecologist may also use this examination to take a small biopsy, felt as a quick pinch, for further analysis.
If abnormalities in the cells persist after colposcopy, there are other methods of excising the abnormal cells, such as a "LLETZ" treatment or a cone biopsy, where a layer around the transformation zone is removed under local or general anaesthetic.
Contact details:
Information for women and their partners who are concerned about cervical screening or cancer can be obtained from the Irish Cancer Society, via its website, which has a live chat facility, or from trained oncology nurses manning the society's freephone helpline at 1800 200 700. E-mail helpline@irishcancer .ie.
See also:
• www.cancer.ie
• National Cancer Registry: www.ncri.ie
• Irish Cervical Screening Programme: www.icsp.ie
• National Cancer Institute (US): www.nci.nih.gov