3.3 Organised cervical screening is a systematic and
co-ordinated programme designed to invite all women who are eligible
for screening to undergo periodic sampling of the uterine cervix using
the Pap test. The most frequent type of uterine cancer is a carcinoma
of squamous cell type. The cancer develops over time from a pre-cancerous
lesion. Pre-cancerous lesions have not invaded the tissues and are curable
if detected and treated. The Pap test is named for Dr George Papanicolaou
who showed that it was useful in detecting the abnormal cells shed from
pre-cancerous squamous lesions of the cervix. Pre-cancerous lesions
detected by the Pap test are classified as squamous intraepithelial
lesions (SIL) and are subdivided into low-grade (LSIL) and high-grade
(HSIL) lesions. The lesions differ in the degree of cellular abnormality
and while both lesions can progress to cancer if untreated, the rate
and interval varies. Cells of HSIL are more abnormal and the lesions
progresses to cancer more frequently and faster than LSIL lesions. Pre-malignant
lesions in biopsy samples of the cervix are also classified as LSIL
and HSIL. Sometimes, however they are classified as CIN (cervical intraepithelial
neoplasia) and depending on the degree of involvement of the cervical
lining by the abnormal cell proliferation, CIN is graded as CIN I (lower
one third of the lining), CIN II (lower two thirds of the lining) and
CIN III (upper one third or full thickness of the lining). Occasionally
Arabic numerals are used instead of Roman numerals. LSIL equates with
CIN I and HSIL encompasses CIN II and CIN III. The CIN terminology is
sometimes used in addition or as a substitute for the SIL terminology
in the reporting of abnormal smear tests.
3.4 A screening programme can be an effective tool
to reduce the incidence of cervical cancer. If pre-cancerous abnormalities
are detected and treated before they progress to cervical cancer the
outcome for the patient will usually be good. However, these abnormalities
are not easily detected by the patient or her clinician. Because they
display no symptoms or signs there is nothing to alert a woman and as
the pre-cancerous abnormalities are not visible to the naked eye her
clinician is not likely to detect them on any visual examination of
the cervix. Regular cervical smear tests should lead to the discovery
of these abnormalities before the development of cancer. A Bulletin
of the World Health Organisation 64(4): 607-618 (1986) titled Control
of Cancer of the Cervix Uteri records that a 100% cure rate is possible
if the presence of the disease is detected, diagnosed and treated during
the pre-invasive stage. The European guidelines for quality assurance
in cervical cancer screening, which were issued in 1993, state that
91% of squamous cell invasive cervical cancer cases can be avoided if
women are screened every third year.
3.5 If a screening programme is to be successful cervical
smear tests must be accurately read by the laboratory. Reading cervical
smear tests is not a precise science. The interpretation of cervical
smear tests is somewhat subjective and in some cases a smear test can
be open to different interpretations. Pathologists accept that errors
can occur and that occasionally a cervical smear test will be misread
as a false negative or a false positive. A false negative result is
one, which fails to identify someone who has a pre-cancerous abnormality
or cancer of the cervix. A false positive result is one, which incorrectly
identifies someone as having a pre-cancerous abnormality or cancer of
the cervix. False positives will be detected because a positive smear
test report will usually be followed by a biopsy (the taking of a tissue
sample from the cervix) and examination of the sample would reveal no
cervical abnormality. False negatives are more difficult to detect as
here an abnormal cervical smear test is misread as normal, and so it
may go undetected until the woman next has a cervical smear test or
has a biopsy of her cervix. A false positive cervical smear test can
lead to a woman undergoing an unnecessary medical intervention in order
to obtain a sample of tissue from her cervix. A false negative cervical
smear test means the presence of a pre-cancerous abnormality will go
undiscovered; this leaves a woman vulnerable to developing cervical
cancer.
3.6 False negative reports do not only result from
errors by pathologists or cytoscreeners. Other reasons may be that the
smear was not taken adequately or that even though the smear was taken
correctly none of the abnormal cells present were included. In a screening
programme where a woman is being screened at regular intervals a false
negative result will often be remedied by detection at the next screening.
Cervical cancer is usually a slow-developing disease and in most cases
the single under-reporting of a cervical smear test will not endanger
a woman’s health or life. Pre-cancerous abnormalities of the cervix
can regress naturally; and if there is no regression, so long as the
abnormality is detected at the next screening or before it has progressed
to cervical cancer it can usually be treated successfully. Though, the
longer the abnormality is left untreated the greater may be the thickness
to which it has involved the cervical lining, in which case the patient
will undergo a more invasive form of treatment than she may have undergone
if the abnormality had been detected sooner. However, if a series of
cervical smear tests of a patient are under-reported the consequences
for that patient can be dire as once the disease has progressed to cervical
cancer the necessary treatment has a severe impact on the patient and
its outcome is more problematic.
3.7 Another respect in which accurate smear test reports
are important is their impact on how a patient is treated. Because of
the possibility of regression, particularly in the case of LSIL (a low-grade
abnormality), the medical response to discovery is often to wait and
see what develops. As HSIL (high-grade abnormality) has a higher rate
of progression to cancer and a lower regression rate, standard practice
is to refer the woman for colposcopic examination. Standard practice
in New Zealand was for the pathologist reading the abnormal smear test
to include in the report a statement with regard to the further management
of the woman. This statement was dictated by the smear findings. The
colposcope is an instrument that magnifies the cervix and allows easier
visualisation and biopsy of cervical abnormalities. Treatment is primarily
guided by the result of the biopsy. Treatment options for pre-cancerous
lesions include ablation of the lesion using laser or cryotherapy. Treatment
for some lesions may require wider removal of the abnormal tissue and
this may involve a cone biopsy, which can be performed using a knife,
laser or electrocautery.
3.8 The Committee has learnt that some women regard
these investigations and procedures as intrusive and unpleasant. Consequently
a clinician will be reluctant to subject a patient to these procedures
if an alternative approach is tenable. A clinician has to weigh the
consequences for the patient of delaying investigation against the intrusion
the patient may feel if referred for further investigation. Thus it
is important for the patient’s clinician to be given a smear test report
which identifies accurately the grade of any abnormality that is present.
3.9 Because under-reporting of cervical smear tests
can not be avoided the difficulty for health professionals and authorities
is to be able to distinguish the false negative tests that are an accepted
feature of cervical screening from unacceptable under-reporting. Errors
of the latter type can all too easily be mistaken for false negatives
which come within the acceptable range. Until a pattern of errors, which
suggests something worse than the accepted false negative rate comes
to light, an unacceptable level of under-reporting is difficult to detect.
By the time such errors are detected the health of the women whose cervical
smear tests have been under-reported may be in jeopardy. Detection of
unacceptable under-reporting is made more difficult in New Zealand
by the absence of any standard which defines the range of acceptable
under-reporting. The consequence is that unacceptable under-reporting
may go unrecognised until such time as it becomes glaringly obvious.
3.10 Cases of symptomatic cancer of the cervix, especially
of advanced disease, in a screened population can be described as failures
of a screening programme. The evidence the Committee heard from women
who had participated in the National Cervical Screening Programme for
a number of years and whose cervical smear tests had been under-reported
makes plain the human consequences of a screening programme failure.
Their evidence was a stark reminder of the injurious impact the failure
of a screening programme can have on its participants.
