A study of the effect of introducing a restrictive cervical screening policy on laboratory workload and cervical cancer detection rates

This study examines the effect of a change in screening policy on the detection rate of severe dyskaryosis. During 1987 a total of 423 cases of severe dyskaryosis were identified by the Avon Screening Programme. Eleven per cent of these abnormal smears were repeat smears taken without clinical indication within the recommended 5 year recall period (interval smears). In a comparable control group of negative smears 31% were interval smears. Twenty-five per cent of the dyskaryotic interval smears (3% of the total severely dyskaryotic smears) were taken within 3 years of the previous negative smear, compared with 50% of the control group. By discouraging opportunistic smears within 5 years of the previous smear, the laboratory workload could be reduced by 30%, or within 3 years of the previous smear by 15%. There is, however, a risk of 11% and 3% respectively of missing a significant lesion (severe dyskaryosis).     

Achievable standards, Benchmarks for reporting, and Criteria for evaluating cervical cytopathologySecond edition including revised performance indicators

Endocervical cells are not essential for an adequate smear, except where the previous abnormality was seen in endocervical cells. When three consecutive smears are reported as inadequate, the recommendation for colposcopy should be made at the discretion of the pathologist in the light of a review of the relevant slides and the clinical history of the woman concerned. The cellularity of previous sequential smears should not be combined in order to judge the present smear test as negative. There should be no more than three abnormal smears (including borderline) over any 10-year period without a recommendation for colposcopy. At least three negative smears, at least 6 months apart, should be reported before a woman is returned to routine recall following a smear showing mild dyskaryosis or borderline nuclear change. There is no evidence that demonstrates that selective double screening is any more effective in preventing false-negatives than rapid review and this practice cannot therefore be justified. Sensitivity should be based on all abnormalities detected on primary screening rather than on moderate dyskaryosis or worse. Ranges for reporting rates are based on the 10-90th percentiles of the range for laboratories reporting over 10000 screening smears per year in KC61 returns, but apply to all laboratories reporting screening smears.     

Comparison of cytology and histology results in English cervical screening laboratories before and after liquid‐based cytology conversion: do the data provide evidence for a single category of high‐grade dyskaryosis?

R. G. Blanks and R. S. Kelly
Comparison of cytology and histology results in English cervical screening laboratories before and after liquid‐based cytology conversion: do the data provide evidence for a single category of high‐grade dyskaryosis? Objective: To determine whether the difference between the positive predictive value (PPV) for cervical intraepithelial neoplasia (CIN) grade 2 or worse (CIN2+) of referral from moderate dyskaryosis and from severe dyskaryosis was reduced after laboratories converted from conventional to liquid‐based cytology (LBC). Furthermore, to explore the cytology/histology agreement after LBC conversion, and to determine post‐LBC whether there was increased support for the use of one single category of high‐grade dyskaryosis (equivalent to high‐grade squamous intraepithelial lesion). Methods: The association between cytology and histology has been examined using annual Korner return data (KC61 returns) collected by laboratories from the English National Health Service cervical screening programme. The study compares return data before and after LBC conversion. Results: The study examined data from 102 laboratories that converted from conventional cytology to LBC. Before conversion the PPV for CIN2+ of severe dyskaryosis was 88% and after increased to 90% (P = 0.003). For moderate dyskaryosis the PPV for CIN2+ increased from 70% to 72% (P = 0.06). The absolute difference of 18% between severe and moderate dyskaryosis was therefore the same pre‐ and post‐LBC conversion. The PPV of mild dyskaryosis for CIN2+ before and after conversion reduced from 23% to 19% (P < 0.001). The agreement between cytology and histology measured using a weighted Kappa statistic increased from 0.52 to 0.60 after conversion to LBC because of small increases in the proportions of severe dyskaryosis or worse with CIN3+ outcomes and mild dyskaryosis with CIN1 or less outcomes. Conclusions: Following LBC conversion there was evidence of a modest increase in the agreement between cytology and histology but no evidence of a change in the absolute difference in PPV for CIN2+ between moderate and severe dyskaryosis. The data support the conclusion that women referred with moderate dyskaryosis will on average have a lower risk of progression to invasive cancer than women referred with severe dyskaryosis. If the data were considered to support the categories of high‐grade dyskaryosis (moderate) and high‐grade dyskaryosis (severe) before LBC conversion then it can be strongly argued that they also support these categories after conversion.     

Using a graph of the abnormal predictive value versus the positive predictive value for the determination of outlier laboratories in the National Health Service cervical screening programme

R.G. Blanks Using a graph of the abnormal predictive value versus the positive predictive value for the determination of outlier laboratories in the National Health Service cervical screening programme. Objective: The positive predictive value (PPV) for the detection of cervical intraepithelial neoplasia (CIN) grade 2 or worse of referral to colposcopy from moderate dyskaryosis or worse (equivalent to high‐grade squamous intraepithelial lesion or worse) is a standard performance measure in the National Health Service cervical screening programme. The current target is to examine ‘outlier’ laboratories with PPVs outside the 10th–90th percentile, which automatically identifies 20% of laboratories for further investigation. A more targeted method of identifying outliers may be more useful. Methods: A similar measure to the PPV, the abnormal predictive value (APV), can be defined as the predictive value for CIN2 or worse for referrals from borderline (includes atypical squamous and glandular cells) and mild dyskaryosis (equivalent to low‐grade squamous intraepithelial lesion) combined. A scatter plot of the APV versus the PPV can be produced (the APV‐PPV diagram). Three kinds of ‘outlier’ can be defined on the diagram to help determine laboratories with unusual data. These are termed a true outlier value (TOV) or an extreme value (EV) for either PPV or APV, or a residual extreme value (REV) from the APV‐PPV best line of fit. Results: Using annual return information for 2007/8 from 124 laboratories, two were defined as having EVs for PPV (both had a relatively low PPV of 62%). For APV, four laboratories were considered to have EVs of 34%, 34%, 34% and 4% and one was considered to be a TO with an APV of 45%. Five were identified as REV laboratories, although three of these were also identified as having extreme or outlier values, leaving two that had not been identified by the other methods. A total of eight (6%) laboratories were therefore identified as meriting further investigation using this methodology. Conclusions: The method proposed could be a useful alternative to the current method of identifying outliers. Slide exchange studies between the identified laboratories, particularly those at opposing ends of the diagram, or other further investigations of such laboratories, may be instructive in understanding why such variation occurs, and could therefore potentially, lead to improvements in the national programme.     

Monitoring and evaluating the performance of the UK NHS Cervical Screening Programme: monitoring performance by using cytology outcomes adjusted for population characteristics

Current quality assurance measures used in the NHS cervical screening programme (NHSCSP) include a review of laboratories with percentages of moderate/severe and borderline/mild smear results outside the 10th-90th percentiles. The method is limited by the fact that many of these outlier smear percentages may reflect laboratories covering populations with low or high risk and/or short or long average screening intervals. This paper outlines a new approach to aid the detection of outlier laboratories, by using data collected at the primary care trust (PCT) or health authority (HA) level and making allowances for population characteristics and screening interval. The setting is the NHSCSP in England using annual data provided by HAs. Data from the screening year 2000-01 is used to illustrate the methodology, although the methods can also be applied to data at the PCT level (now being collected for 2002-03 onwards). Percentages of smear results have been analysed against a series of explanatory variables using logistic regression models. These explanatory variables include Townsend deprivation index, uptake-corrected ethnic minority composition, a measure of screening interval, area type and region. An expected percentage of borderline/mild and moderate/severe smears is estimated from the models and an observed : predicted ratio (OPRmod/sev and OPRbord/mild) calculated. Low values are suggestive of relative undercalling and high values overcalling, after allowance for population characteristics. Analysis of data for 2000-01 showed that the OPRmod/sev for the 99 HAs varied from 0.68 to 1.44. Laboratories with low percentages of moderate/severe smears, but associated with PCTs or HAs with OPRmod/sev values closer to unity may not need to be investigated as their observed rates are consistent with predicted rates based on population characteristics. The method could also be directly applied to laboratories if further information on the population covered by each laboratory were routinely collected.     

ABC3 Part II: a review of the new criteria for evaluating cervical cytology in England

R.G. Blanks
ABC3 Part II: a review of the new criteria for evaluating cervical cytology in England The new Achievable Standards, Benchmarks for Reporting, and Criteria for Evaluating Cervical Cytopathology, 3rd edn (ABC3) includes radical changes in the criteria for evaluating cervical cytology. First, they include a new mission statement ‘the objective of cervical screening is to reduce cervical cancer incidence and mortality by screening with a high sensitivity for the detection of CIN2 or worse, whilst maintaining a high specificity’. Second, the original four performance measurement criteria where laboratories were examined further if they were below the 10th or above the 90th percentile has been changed to three and laboratories are only mandatorily examined if they fall below the 5th or above the 95th percentile. The old criteria related to the percentage of samples that were inadequate, the percentage of all adequate samples reported as moderate dyskaryosis or worse (equivalent to high‐grade squamous intraepithelial lesion or cancer), the percentage of adequate samples reported as mild dyskaryosis or borderline (equivalent to low‐grade squamous intraepithelial lesion or atypical squamous/glandular cells) and the positive predictive value. The new criteria are percentage of inadequate samples, positive predictive value and a new measure termed referral value. These changes mean that far fewer laboratories will require mandatory examination. Third, a raft of optional performance measures have been introduced to help laboratories examine their annual statistical return to the Department of Health in comparison with other laboratories. These measures have been designed to produce a more uniform national programme, and to help laboratories decide whether they are maximizing the benefit of screening while minimizing the harm, which is the goal of all screening programmes. This review examines in detail the new criteria and explains in more detail some of the thinking behind them.     

Koilocytosis; an indication for conservative management

The management of women with mild dyskaryosis continues to be the subject of debate. The management of cases with such smears could be improved if additional morphological features were found to be indicative of low/high grade cervical intraepithelial neoplasia (CIN). Our own experience in the routine audit of the diagnostic accuracy of cervical smears had suggested that cases of dyskaryosis with koilocytosis were associated with a low risk of CINIII. Two hundred and forty-four cervical smears reported as showing evidence of wart virus infection were reviewed and their subsequent histories noted. Of these smears, 173 demonstrated clear evidence of koilocytosis. Irrespective of the initial grade of dyskaryosis, only 28 cases (16.2%) had underlying CIN or had progressed to CIN over a minimum follow-up period of 21 months. Only two cases (1.2%) showed evidence of CINIII. Koilocytosis is associated with a low risk of CIN and an especially low risk of CINIII. The management of women with koilocytic smears should be modified accordingly.     

Liquid-based cytology and conventional smears compared over two 12-month periods.

BACKGROUND AND OBJECTIVE: Liquid based cytology (LBC) was introduced across the Scottish Cervical Screening Programme in 2003-2004. The objective of this study was to compare in a large cytopathology laboratory the results of cervical samples over two twelve-month periods, 2001-2002, when the great majority of smears were conventional, with 2003-2004, when all were LBC. METHODS: The results of smears in both periods were analysed to give overall reporting profiles, and correlated with results of cervical biopsies. The numbers of patients referred for colposcopy were compared. RESULTS: The percentage of unsatisfactory smears fell from 13.6% to 1.9%. Colposcopic referrals for repeated unsatisfactory smears fell from almost 25% to 0.5%. There was a decrease in overall smear numbers, but despite this there was an increase in the number of smears reported as showing dyskaryosis of any grade. There was an increase in positive predictive value for moderate dyskaryosis and above, from 79.5% to 86.1%. The outcome of biopsies from patients referred with mild dyskaryosis showed no decrease in accuracy of predicting a low grade histological lesion. Workload in the laboratory decreased, due to fewer smears received overall, more rapid primary screening times and fewer multi-slide cases. Primary screening backlogs all but disappeared, and reporting times greatly improved. CONCLUSIONS: Introduction of liquid based cytology led to improvements in unsatisfactory smear rates, with significant benefits to colposcopic referrals and laboratory turnaround times. Pick-up rates of dyskaryosis were maintained, and the positive predictive value of a dyskaryotic smear report was improved.     

The effect of nonscreening smears on screening smear results: a statistical analysis with its implications for the NHS cervical screening programme

This is a statistical analysis of individual NHS Cervical Screening Programme laboratories screening smear 'pick-up' rates (defined here as percentage low grade and percentage high grade of total adequate smears for ages 20-64 years derived from general practitioners and community clinics) in relation to their nonscreening smear workload proportion (here defined as percentage nonscreening smears of total laboratory workload from all sources for all ages). This was achieved by the use of three one way ANOVA models in order to receive a complete overview of the results. The models were applied to the following: (1) Laboratories with a total workload of less than 15000 general practitioner (GP) and community clinic smears; (2) laboratories with a total workload of greater than 15000 GP and community smears and; (3) all laboratories (i.e. a combination of 1 and 2). The 'test' groups within each of these models comprised three subgroups based on the percentage of laboratory workload that consisted of smears from a nonscreening source. This figure ranged from 2.8% to 82.6%. The subgroups were divided so as to contain approximately the same number of laboratories in each one (172 laboratories in total, 42 with workload < 15000 and 130 with > 15000). The results show that laboratories high and low grade pick-up rates have a positively correlated but variable relationship with the proportion of their workload that consists of nonscreening smears. The results show significance overall at the 5% level for high grade and the 10% level for low grade (high grade at P = 0.045 and low grade at P = 0.071). Significance for laboratories viewing less than 15000 screening smears at the 1% level (high grade P = 0.006 and low grade P = 0.005). They show no significance, however, for laboratories viewing more than 15000 screening smears (high grade P = 0.457 and low grade P = 0.622). There is an intriguing possibility that a greater exposure to abnormal smears results in a greater tendency to detect them. The current data provides no evidence to support the NHS Executive's use of 15000 as a designated figure when quality monitoring and service provision becomes a specific issue. The closure or amalgamation of laboratories with workloads less than this would appear to have no scientific evidence base.     

Koilocytosis; an indication for conservative management

The management of women with mild dyskaryosis continues to be the subject of debate. The management of cases with such smears could be improved if additional morphological features were found to be indicative of low/high grade cervical intraepithelial neoplasia (CIN). Our own experience in the routine audit of the diagnostic accuracy of cervical smears had suggested that cases of dyskaryosis with koilocytosis were associated with a low risk of CINIII. Two hundred and forty-four cervical smears reported as showing evidence of wart virus infection were reviewed and their subsequent histories noted. Of these smears, 173 demonstrated clear evidence of koilocytosis. Irrespective of the initial grade of dyskaryosis, only 28 cases (16.2%) had underlying CIN or had progressed to CIN over a minimum follow-up period of 21 months. Only two cases (1.2%) showed evidence of CINIII. Koilocytosis is associated with a low risk of CIN and an especially low risk of CINIII. The management of women with koilocytic smears should be modified accordingly.     

Posters. P11 Positive predictive values for high and low‐grade cytological abnormalities as surrogates for specificity and sensitivity

Introduction Positive predictive value (PPV), measuring the percentage of moderate dyskaryosis or worse confirmed as CIN2 or worse, is used as a measure of accuracy in cervical screening. However, it relates more to specificity than sensitivity because the denominator includes false positives rather than false negatives. Low values reflect over‐reporting of high‐grade dyskaryosis but high values may reflect under‐reporting. Sensitivity is impossible to measure from correlation of cytology with outcome because women with negative cytology are rarely referred for colposcopy. Rates of CIN3 resulting from referrals for low‐grade cytology may be used as a surrogate for sensitivity, as high values may reflect under‐reporting (ref). Study design Outcome of colposcopy referrals was monitored during a period of 4 years, using a fail‐safe database. Results PPV at Guy's & St Thomas rose from 54% in 1998/1999 to 69% in 2001/2002. The former was below the NHSCSP recommended range. During the same period of time CIN1 rates for moderate dyskaryosis fell from 37% to 24%, reflecting the main source of discrepancy. While specificity increased (as reflected by increasing PPV) sensitivity remained constant in that CIN3 rates for mild dyskaryosis and borderline remained below 6%: average rates in England have fallen over the last 3 years and were 7.4% in 2000/2001 (ref). CIN2 rates for mild dyskaryosis also remained constant at 11% to 12%. Conclusion Correlation of biopsy results with high‐ and low‐grade cytological abnormalities is a useful method of monitoring accuracy of cytology reporting, and can be used to measure over‐ and under‐reporting as surrogates for specificity and sensitivity.     

Interlaboratory reproducibility of atypical glandular cells of undetermined significance: a national survey

OBJECTIVE: The aim of this study was to evaluate the inter-laboratory reproducibility for atypical glandular cells (AGC) (The Bethesda System (TBS) 2001) of the laboratories involved in the screening programmes in Italy. METHODS: A set of 35 selected slides were circulated among 167 laboratories involved in local population-based cervical screening programmes. Each laboratory provided one single diagnosis per smear. The smears were read blind to the original diagnosis and to the diagnoses provided by other laboratories. A 'majority' diagnosis was defined for each case and assumed as the reference standard. The diagnosis provided from each laboratory was compared with the majority diagnosis. RESULTS: According to the majority report the 35 slides in the set were classified as negative in nine cases, AGC in eight, adenocarcinoma in eight, and squamous lesion or squamous + glandular lesion in 10. The crude agreement between all pairs of laboratories was 49.43%. K-values were 0.46, 0.21, 0.34, 0.36 and 0.32 for negative, AGC/AIS (adenocarcinoma in situ of endocervix), AdenoCa, Sq/Sq + Gl and all reporting categories respectively. Concordance according to overall K was moderate to substantial in 77% of the participating laboratories. CONCLUSIONS: The present study shows that the AGC category is not easily reproducible. The data confirmed the importance, in a screening scenario, of AGC/AIS diagnoses, but also presented difficulties in differentiating between the two diagnoses. In addition to the results obtained from the circulation of the slides, laboratories which had annually a low number of cervical smears were able to gain experience focused on particular morphological pictures.     

The use of the 'borderline' category in the reporting of cervical cytopathology in the UK: results of a survey conducted under the aegis of the British Society for Clinical Cytology

Objective: To determine how the ‘borderline’ category was used by cytopathologists in the UK when reporting cervical smears. Methods: A questionnaire was sent by email to members of the British Society for Clinical Cytology. Results: There is wide variation in the use of the ‘borderline’ category in the UK but the majority of respondents (77.6%) used it when reporting smears that were either on the borderline between negative and low grade squamous dyskaryosis (‘borderline ?low grade’), or on the borderline between negative and high grade squamous dyskaryosis (‘borderline ?high grade’), or on the borderline between negative and glandular dyskaryosis ‘borderline ?glandular dyskaryosis’). A significant minority (15.7%), however, did not use ‘borderline’ when reporting smears that showed an abnormality that was possibly high grade squamous dyskaryosis. A majority (79.1%) of respondents thought that it would be useful to have separate reporting categories for ‘borderline ?low grade’ and ‘borderline ?high grade’. Conclusions: There is diversity in the use of the category ‘borderline’ in the UK. The proposed revised BSCC terminology with separate categories for borderline ?low grade, borderline ?high grades and borderline ? glandular dyskaryosis reflects the opinion of the majority of respondents to the questionnaire.     

Rapid Cervical Cytology Screening

2030 Papanicolaou-stained cervical smears were submitted for rapid screening prior to routine screening; 30 seconds were allowed for each slide, and those thought to be abnormal were identified. The results were compared with those of conventional screening. All severe and moderately dyskaryotic cases were detected by the rapid technique, as were the majority of mild dyskaryosis and borderline cases. When a laboratory has a backlog it may be worth rapid-screening all slides in addition to routine screening, so that patients most at risk can receive prompt treatment.     

Six years' audit of laboratory workload and rates of referral for colposcopy in a cervical screening programme in three districts.

OBJECTIVE--To determine laboratory workload and rates of referral for colposcopy in a three district cervical screening programme during 1983-9 to assess the feasibility of accommodating call up of all women at risk, recall at three year intervals (now five year intervals), and investigation of women with all degrees of abnormality. DESIGN--Analysis of computerised screening histories dating back to 1977 of women screened in the Avon cervical screening programme. SETTING--Three district health authorities covering the population of Bristol and Weston-super-Mare, comprising 800,000 people, of whom 250,000 were female residents aged 20 to 64. SUBJECTS--196,977 Women aged 20 to 64 screened in cervical screening programme since 1983. RESULTS--Laboratory workload devoted to follow up of women with abnormalities increased sharply between 1987-8 and 1988-9, with increases of 54% (from 2075 to 3196) in the number of smears for follow up of severe dyskaryosis and invasive cancer, 40% (from 1925 to 2695) for mild and moderate dyskaryosis, and 49% (from 1793 to 2677) for borderline change. The increases were partly explained by the introduction in April 1988 of protocols for follow up and investigation based on guidance in an intercollegiate working party report. The proportion of women with mild and moderate dyskaryosis who were recommended for referral for colposcopy increased steadily from 9.9% in 1983-4 to 79.9% in 1988-9, and for borderline change the proportions were 3.5% and 13.6% respectively. Of all women tested in 1988-9, referral for colposcopy was recommended in 3%. CONCLUSIONS--The increase in laboratory follow up work identified, if it continued, could result in half of existing laboratory capacity in Avon being devoted to follow up work by 1993, with little prospect of maintaining call, recall, and quality control. Investigation of all women with minor cytological abnormalities is neither justifiable nor sustainable and will undermine the benefits of screening by increasing the rate of false positive results and the financial costs.     

An audit of the positive predictive value of high-grade dyskaryosis in cervical smears: 2001–2002

The positive predictive value (PPV) of high-grade dyskaryosis for cervical intraepithelial neoplasia grade 2 (CIN2) or worse on histology is published annually for the laboratories in the UK National Health Service Cervical Screening Programme (NHSCSP). The PPV fell in 2001 compared with 2000 for four of the five consultants reporting cervical smears in our laboratory, the greatest fall being from 91.6% to 77.9%. Investigation of the possible reasons for the fall suggested the main cause lay outside the laboratory in the type of biopsy taken at colposcopy. We conclude that biopsy type affects accuracy of PPV calculations. There is variation in collection and submission of KC61 data including PPV across laboratories. This factor needs to be taken into account when publishing and comparing laboratory data for the NHSCSP.     

Performance of the DNA-Citoliq liquid-based cytology system compared with conventional smears

OBJECTIVE: To evaluate the performance of a new, manual, simplified liquid-based system, DNA-Citoliq (Digene Brasil), employed under routine conditions as compared to conventional smears collected from six collaborating private laboratories. METHODS: A panel of cytopathologists, who served as the gold standard diagnosis, adjudicated discordant opinions. RESULTS: Of 3206 pairs of slides considered valid for comparison, there were 3008 in full agreement (93.8%), 112 (3.5%) with one diagnostic category discrepancies, and 86 (2.7%) discordant cases. Among the 288 borderline+ by either method, DNA-Citoliq detected abnormalities in 243 (84.4%), and conventional smears (CS) detected abnormalities in 178 (61.8%) (McNemar test, P < 0.000), a 36.5% increased detection of borderline+ cases. CONCLUSIONS: For mild dyskaryosis, DNA-Citoliq detected 176 cases and CS 125 cases (McNemar test, P < 0.000); and for moderate+severe dyskaryosis 66 versus 32 cases respectively (McNemar test, P < 0.000).     

The Cardiff Cervical Cytology Study: prevalence of cytological grades and initial histological findings.

Among 45 266 women in the Cardiff Cervical Cytology Survey the peak prevalence of suspicious or positive smears was 11.2/1000 at age 45-50 years and of dyskaryosis 10.2/1000 at age 25-29. A suspicious or positive cytological picture at prevalence testing was associated with occult or clinical invasion in 24% of cases, and only 4% of patients with suspicious or positive smears were normal histologically. When dyskaryosis was detected in the prevalence test 20% had carcinoma in situ or microinvasion and 3% had occult or clinically invasive carcinoma. One hundred and twenty-nine (51%) women with dyskaryotic smears did not have a biopsy initially (that is, within two years of the prevalence test), but they were followed up at regular intervals. Subsequently 15 of the 129 gave smears consistently dyskaryotic or worse cytologically and were subjected to biopsy. Of these, two showed dysplasia, 12 carcinoma in situ, and one clinically invasive carcinoma. These findings emphasise the need for repeat cytological or histological examination in any woman with evidence of dyskaryosis in a cervical smear.     

Quality grading for cervical smears

Three thousand five hundred and eighty cervical smears were taken in 1990–1992 at a Genitourinary Medicine Clinic with various spatula or spatula brush combinations. the unsatisfactory rate and the detection of cellular abnormalities showed some relation to spatula type. However, the satisfactory smears screened in the laboratory are routinely assigned a quality grade-good, fair or poor. Analysis shows higher rate of detection of cellular abnormalities in good quality smears, the detection of dyskaryosis being twice as high, in contrast to the fair or poor quality smears. It is suggested that quality grade is a better way of classifying smear quality in the cervical screening programmes rather than the presence or absence of endocervical and/or metaplastic cells.