Cytology as a Cervical screening Test: How effective is it?
S. Bomfim Hyppolito
Objective : To assess the effectiveness of cytology Pap smear as a screening test to early detection of Low and High Grade Squamous Intraepithelial Lesions (LHSIL and HGSIL) and cervical cancer, as well.
Search strategy : A computerized Medline search and a manual literature
search of a relevant unpublished paper.
Data collection and analysis : Data were extracted by the reviewer and any discrepancy was discussed with the senior advisor and modified.
Main results : Eight randomized or quasi randomized trials published during the last ten years investigating different Kind of cervical collection devices and slide preparation techniques, and comparing also HPV-DNA and cervicography tests with Pap smear test demonstrated that: Pap smear sensitivity medium rate is around 60% (29 to 80%).
Conclusions : Pap smear is just a screening test and is subjected
to limitations. It reduces the incidence of cervical cancer but it is not
expected to detect all the precursor lesions and it is not appropriate to
detect large invasive neoplasias.
Although efforts to reduce the health impact of cervical cancer have been initiated in countries all over the world, most attempts in developing countries have not been successful due to such factors as limited access to necessary health interventions, and inability to provide accurate Pap smear services to all those who need them.
Since 1943 when Papanicolaou and Traut proposed a new technique - Pap smear test - to detect precursors of cervical cancer in women, cytological screening has been one, and probably the most successful of several public health measures introduced for the prevention of cancer. On the other hand, the effectiveness of this screening technology is taken for granted, and this may have been a mistake. The quality of Pap smear can be influenced by many factors, including the technique of collecting the cells from the cervix and the method of preserving and handling the smear plus the accuracy of data interpreters. The perception that the Pap smear is infallible has led many to believe that a negative test means the absence of cervical cancer.
Recent data (Melamed MR et al, 1998) from International Academy of Cytology Task Force shows that the undetected abnormalities rate is around 10-35% of abnormal Pap smear slides. This means that one out of every five or one out of every four abnormalities are not detected. Other more comprehensive studies (Hussein Y et al, 1997) shows results between 20 and 30%. This corresponds to sensitivity rates of 70% to 80%.
Cervical screening has been proven to be effective in decreasing the incidence of invasive disease where comprehensive programs exist (Parkin 1985, Duguid 1985). In spite of this, cervical cancer is still an important reproductive health problem in women, especially in developing countries where at least 200.000 women die from the disease each year.
It has become a consensus nowadays that the adequacy of a cervical smear is considered when there is the presence of endocervical cells, since their presence means the transformation zone, from which premalignant change arises, has been catched. It seams to be a reliable assumption, as the updated Cochrane review study (Martin-Hirsch P, et al 1997) on cervical smear collection devices concluded, that the widely used Ayre spatula is the least effective device for cervical sampling and that it should be replaced by the Aylesbury spatula because it allows better endocervical collection sample. So, they have agreed , detection rates of endocervical cells appear to be a valid and convenient surrogate for the ability to detect dyskaryosis. Ayre spatula is the more commonly used device on several countries, including Brazil, and cytopathology labs are not considering the inclusion of endocervical cells in the smear as a quality standard issue. Other authors (Kristensen GB et al,1989) advocate that a large-scale application of the spatula-cytobrush method should result in fewer repeat smears required and fewer false-negative tests.
Additionally the location of the transformation zone varies; it moves towards ectocervix during reproductive life and is indrawn in the endocervix with menopause. So the appropriateness of the sampling instrument is bests determined by the characteristics of the women’s cervix and the location of the transformation zone.
Even if one collects adequate Pap smear, poor transfer of the cells to the slide may result in a sample either too thick or uneven for accurate exam. Many investigators ( Hutchinson ML et al, 1992) are now testing and proposing different smears preparation techniques such as the monolayers system and comparing it to conventional preparations. According to Noorani H Z, 1997, these techniques may increase the effectiveness of the Pap test. The collection of cervical cells remain the same, but the cells are rinsed from the collection device into a vial of preservative solution. Automated process gently disperse the sample, then separate cervical epithelial cells from debris by filtration (ThinPrep) or density gradient centrifugation (CytoRich). The results seem to reduce inadequate smears, but increases cost, becoming not feasible to include on Cervical Cancer detection screening programs in developing countries.
Each smear might contains approximately 300.000 epithelial cells and at least 5 minutes careful look is required for each slide reading. It is impossible for a cytotechnologist to screen with accuracy a large number of smears a day. As developing countries have few lab resources, they are also usually overloaded and there are also very few persons who are well trained to read the slides. To improve screening profile requires a selective screening program and a continuing training program for cytotechnologists. Several authors (Schneider A, 1996) ,though ,are proposing screening for cervical intraepithelial neoplasia grade 2/3 can significantly be improved by Human Papillomavirus (HPV) testing. Some authors (Dunggan et al, 1998) understand that other risk factors such as the age of the women and a history of cigarette smoking were significant predictors of triaged co-incidental CIN II/III and would limit the adoption of HPV testing as an universal, adjunctive test for the identification of those cervical neoplasias. Sideri M et al, 1998 also found that the classification model based in the demographic and lifestyle variables showed comparable results with molecular hybridization for HPV, so that it appears to be a simple and economic possibility for triaging patients with mild dyskaryotic smears in a screening program. So, other alternative strategies can be conducted to enhance Pap smear screening profile.
The importance of laboratory quality is recognized. However there are not yet consistent and systematic guidelines for cervical cytopathology laboratories in many countries. Matsuura et al, 1996, suggest that a composite diagnosis with cytology, colposcopy and punch biopsy is necessary for a correct evaluation of cases and thus increasing the accuracy rates of cytology. Others ,such as Hathorne et al, 1997, advocate the evaluation of cytotechnology trainees through a Compucyte Pathfinder database technique which can reasonably evaluate the performance of human resources of labs who interpret Pap test. In one or other way the quality assurance must be met, and it should be on continuous base.
Women usually do not have regular contact with the health care system or do not have regular Pap smear for various reason. The great majority of positive cases are women who have never had a Pap smear test because of lack of information about the need for preventive care or because they have not had access to cervical cancer detection screening test. There must be more comprehensive cervical cancer screening program services and the identification of simple low-cost screening strategies using local people for performing collecting samples or performing other low technology but appropriate tests. That might help to recruit ever screened women and, at the same time would give assess to better follow-up of negative pap test, thus enhancing its sensitivity.
This systematic bibliographic review intends to study to the issues that are specifically addressed to the efficacy of Pap smear as a Cervical Cancer screening test: sensitivity and specificity.
Search strategy for identification of studies
A computerized Medline search was conducted to identify all randomized or quasi-randomized trials which were related to cytology as a cervical cancer screening test with a major preference on the ones published within the last ten years.The methods (matches) for identifying trials in the Medline were as follows:
Methods of the Review
At first the studies were selected taking into account the following issues : Title of the study (objective), Type of study, Number of subjects, Methodology, Institution (setting of the study), Outcomes, Investigators and Publication.
The studies selected were:
Description of the studies
1. Duggan et al, 1998
Objective: To determine the target group through the high-risk prediction approach, to select the CIN I, CIN II cases diagnosed by Pap test for HPV testing.
Study Design: 622 women referred to three hospital-based colposcopic clinics for investigation of a Pap test abnormality interpreted as CIN I were approached and consented to participate in a 33 month prospective study of the natural outcome of CIN I lesions. At the colposcopic examination a cervical scrape/endocervical sampling for routine cytology was performed using Ayre spatula and/or Cytobrush. A second scrape for HPV typing was next taken with a prewashed Ayre spatula. Consensus regarding pathological and colposcopic criteria was reached amongst the clinics. All investigators were masked to the results of the HPV testing. The women were divided into two groups based on the colposcopic impressions and the repeat Pap test. Group A comprised those whose lesions by both investigative modalities was considered to be CIN I or lesser (</=CIN I) and to group B those with CIN II or greater (>/=CIN II).
Findings: Out of 537 women (there were excluded subjects) recruited for the study, group A was comprised of 342 (63.7%) triaged as </= CIN I by combined colposcopic and Pap test, and group B was comprised of 195 (36.3%) women triaged as >/=CIN II. 36,3% of cervical abnormalities classified as CIN I by Pap test were found to be CIN II/III when correlated with subsequent colposcopic directed biopsy. Triaged co-incidental CIN II/III lesions, however tended to have more HPV positive samples and a higher prevalence of HPV 16/18.
2. Bishop JW, 1997
Objective: To compare the CytoRich system with conventional cervical cytology in a university medical center hospital.
Study Design: 2.32 parallel conventional cervical cytology and CytoRich samples were examined as part of a multiple center trial. Same patients conventional and CytoRich slides were submitted to separate cytotechnologists blindly. The results were compared and all nonmatching sample pairs were reviewed again.
Findings: CytoRich slides had 86.7% sensitivity for SIL and 99.1% specificity while the conventional slides had 63.6% sensitivity and 99.7% specificity. The biopsy correlation results were similar for the two methods.
3. Matsuura Y et al, 1996
Objective: To investigate through a long-term follow-up (more than five years) low grade cervical intraepithelial neoplasia associated with HPV infection.
Study Design: During the 10 years from 1984 to 1993, cold knife conization was performed on 151 patients with early cervical neoplasia proven by punch biopsy. The accuracy rates of cytology, colposcopy and punch biopsy were investigated. The cytological samples were obtained by a swabbing technique. All patients with abnormal cervical cytology underwent colposcopic evaluation. Punch biopsy of cervical tissue was obtained from the most severely abnormal colposcopic finding. Conization was performed in cases of severe dysplasia and by microinvasive carcinoma proven by punch biopsy.
Findings: The accuracy rates for severe dysplasia and CIS, microinvasive carcinoma and frankly invasive carcinoma were 65% (69 of 106), 16% (6 of 38) and 43% (3 of 7), respectively. The overall accuracy rate was 52% (78 of 151), Cytological underestimation occurred in 43% of the cases (66 of 151) and overestimation occurred in 5% (7 of 151).
4. Mayeaux J et al 1995
Objective:To determine the reliability of repeat cervical smears (Papanicolaou smears) in patients who have an abnormal initial smear, prospective data were selected on patients being followed up for a previously normal cervical smear.
Study Design: All patients with a cervical smear showing evidence of SIL, any form of atypia, or a second inflammatory smear result after treatment were routinely referred for colposcopy. Patients found on referral to have colposcopic evidence of invasive cancer were referred to the Oncology without biopsy of further workup and were excluded from the study. All cervical smears were obtained with the Unimar Cervex Brush. All Pap smears performed at the time of colposcopy (repeat cytological resting) were interpreted by the staff of the department. Smears were first examined by cytotechnologists. All abnormal smears, all normal smears in patients with previously abnormal smear, and one in 10 of all smears previously examined were reinterpreted by a pathologist. Acetic acid 5% was applied and all acetowhite lesions were noted. Lugol`s solution was sometimes applied to further define abnormalities. After the entire transformation zone had been adequately examined, an endocervical curettage was performed and directed biopsies were taken from the most abnormal-appearing areas of all lesions. All patients referred for colposcopy to the university’s Family Practice Center between August 1989 and June 1993 were considered for this study. Only patients with single, first-time colposcopies who were referred because of abnormal cytological smears were included. Eleven patients with colposcopic findings of invasive carcinoma or inadequate colposcopies also were excluded leaving a study population of 453 patients. The results of the initial and the repeat cytological evaluations were compared. Findings on repeat cytological evaluation were compared with the colposcopically directed cervical biopsy results (colpopathological findings). Sensitivity, specificity, and predictive values were calculated using methods described by Campion and Reid and Soost et al. Correlation coefficients were calculated between the initial and repeat cytological findings and the colposcopic biopsy results.
Findings: The study included a total of 453 patients with a mean age of 26. The calculated sensitivity for this population was 45% when screening for all CIN. When differentiating high grade from low-grade and benign lesion, the sensitivity of the repeat cervical smear (as measured against the reference standard of histologic evaluation of directed biopsy) was only 25%. The specificity of the repeat cervical smear was found to be 80% when the test was used to screen for CIN and 94% when it was used to detect high-grade lesion. The positive predictive value of the repeat cervical smear in delineating high-grade lesions was only 60%; the negative predictive value was 78%. Of the 428 patients, high-grade lesions were found by colposcopically directed cervical biopsy in 110 patients. Of these 110 biopsy-proven high-grade lesions, 75 patients (68%) had low-grade initial cervical smears and 83 (75%) had low-grade or benign repeat cervical smears.
5. Reid R et al, 1991
Objective:To compare three potential screening tests, used alone or in combination. A total of 1012 women aged 18 to 35 years were screened by cytological testing, cervicography, and hybridization for HPV-DNA
Study Design: This prospective survey examined the prevalence of lower genital tract HPV infection in a structured population of 1012 urban and suburban women aged 18 to 35, recruitment being undertaken in both a sexually transmitted disease clinic and private gynecological offices. Patients were then screened for HPV infection and cervical intraepithelial neoplasia, by means of cytological testing, cervicography and DNA hybridization of exfoliated cells. The study population was drawn from two groups: a high risk and a low-risk subset. The high risk sample consisted of 672 volunteers attending a clinic for STD. The low risk portion comprised 340 volunteers, recruited from four different gynecological clinics. Cytological screening was done with a two-slide technique-collection of an endocervical sample with a Zelsmyr Cytobrush and an exocervical sample with a dagger spatula. Results were reported as high-grade positive (CIN II/III or higher), low-grade positive (definitely abnormal, suggestive of well-developed koilocytotic atypia or cervical intraepithelial neoplasia grade I). After the Papanicolaou smear was completed the cervix was swabbed twice with 4% acetic acid and then photographed. Images were interpreted By subsequent projection onto a 10-foot screen, with the observer standing at a distance of 3 feet. The third screening method involved placing the residual cellular material from the Cytobrush and spatula within a special transport solution, for subsequent DNA extraction and Sothern blot hybridization with radiolabeled probes for HPV types 6,11,16,18,31,33,35,42,43,44,45,51,52 and 56. Results were grouped as positive for an oncogenic type (HPV types 16,18,31,33,35,45,51,52 and 56), positive for a low-risk type (HPV types 6, 11, 42 43 and 44), positive for an unknown type, or negative.
Findings: 343 definitely abnormal cervical test results (88 cytological results, 135 cervigrams, and 120 hybridization were concentrated among 298 patients. 123 equivocal cervical screening test results that were not confirmed by Southern blot hybridization. Papanicolaou smears detected 12 of the 23 high-grade lesions. Apart from disappointing accuracy (sensitivity 52%, specificity 92%) cytological screening carried the significant disadvantage of recalling another 76 patients with either low-grade or borderline atypia (only 13 of which contained some oncogenic HPV type) .
6. Schneider A, 1996
Objective: To evaluate the potential value of HPV test in augmenting the sensitivity of Pap smear or cervicographic screening test.
Study Design: A cohort of 967 non pregnant women with a mean age of 37.1 was studied. Those women had no history of conization, hysterectomy, or cervical intraepithelial neoplasia or atypical cytological results in a cervical smear with 1 year before examination. These women underwent routine screening by two gynecologist between August 1992 and October 1993. On examination, first a Dacron-tipped swab was applied to the ectocervix and endocervix and to the posterior vaginal vault to collect cells for HPV analysis. Second, a cytological smear was taken separately from the ectocervix and endocervix with a cotton-tipped swab, with smears being put on separate glass slides. This smear was called the primary screening smear. In patients with a stenotic cervical canal a Cytobrush was used. Cytological smears were sent to five different routine laboratories; smears from each weekday were classified according to the Bethesda System for reporting cervical or vaginal cytological diagnosis. Third, two cervigrams were taken by use of a Cerviscope camera after application of 5% acetic acid to the cervix. All cervigrams were read on a 2x2 m screen, equivalent to a 16 times magnification by one interpreter who was blinded for cytological and hybrid capture results. Positive patients were recalled for colposcopy at an interval of between 21 and 259 days after entry examination. If colposcopy was negative and the entire squamocolumnar junction visible, only a repeat cytological smear and a swab for HPV detection were taken. If the squamocolumnar junction could not be seen, an endocervical curettage was performed. Histologic examination of the biopsy and curettage specimens was done in two pathology laboratories. In addition, all biopsy specimens were reevaluated by an independent pathologist. It was calculated a sample size of 1.000 patients (i.e. it was expected 20 patients with cervical intraepithelial neoplasia grade 2/3, of which 10 had to be detected by cytological study).
Findings: The presence of high-risk HPVs was age dependent with a peak at 20 to 25 years. Of the primary screening smears, 51 were classified as abnormal and were followed up by colposcopy and biopsy. In 34 cases no cervical intraepithelial neoplasia was detected; 22 of these 34 cases had a cytological diagnosis of atypical squamous cells of undetermined significance. No significant differences between the single methods with respect to sensitivity, specificity, and positive or negative predictive value were found. Augmentation of cytological examination by either HPV testing or cervicography showed a significantly increased sensitivity for detection of cervical intraepithelial neoplasia grade 2/3 (p=0.01=; however augmentation by HPV testing decreased specificity less and increased the positive predictive value compared with cervicography.
7. Soost HJ et al,1991
Objective: To exam cytological screening through a large computerized database to validate the sensitivity, specificity and predictive values of cervical cytology
Study Design: The result of 748.871 cytological examinations of 277.842 women from a ten-year period stored in a computer were used in this study. The evaluation of the validity of cytological screening, positive cytological findings (which included cytodiagnosis of dysplasia, carcinoma in situ, invasive carcinoma and questionable findings) were exclusively validated by subsequent histologic examination performed within one year. One or more positive follow-up smear were taken as evidence that the initial cytological screening was probably correct, but were not taken as absolute proof. Negative cytological findings (if no histologic examination was performed within one year) were validated by at least two subsequent cytological smears taken within three years. If both smears were negative, the first diagnosis was assumed to be correct. If a subsequent histologic finding was positive or if one of the two follow-up smear within three years was positive (severe dysplasia, carcinoma in situ, invasive carcinoma or questionable), the first smear was assumed to be FN. Negative findings that were reported with a recommendation for a repeat smear that had positive findings were not considered to be FN.
Findings: It was known the predictive value of a negative cytological examination was determined to be 99.8%; the predictive value of a positive cytological examination was 73.4% for an initial diagnosis of mild-to-moderate dysplasia, 90.6% for a diagnosis of severe dysplasia/carcinoma in situ, 94.5% for a diagnosis of carcinoma in situ or microinvasive carcinoma and 95.5% for an initial diagnosis of invasive carcinoma. Extrapolation from the validated cases to the entire screened population showed an overall sensitivity of 80% and a specificity of 99.4% for cytological screening for cervical cancer. The sensitivity was slightly lower for mild and moderate dysplasia (78.1%) and slightly higher for carcinoma in situ and severe dysplasia (81.4%) and invasive carcinoma (82.3%).
8. Tabbara S et al, 1992
Objective: To evaluate Pap smears, cervical biopsies and HPV-DNA status of patients applying the Bethesda System of classification to cervical squamous lesions.
Study Design: 75 consecutive biopsy specimens accessioned from the Colposcopy Clinic at the University of Virginia were selected for analysis. Cases were obtained principally from the practitioners or clinics supervised by three of the investigators. Biopsies were reviewed and classified as low-grade, high-grade, or nondiagnostic of an intraepithelial lesion . Distinction of low grade from high grade was based upon the distribution and quality of the nuclear atypia in the lesional epithelium. The criteria for low grade included the presence of either flat or exophytic condylomata, which were characterized by either macular or verrucous lesion in which cytological atypia was confined to the maturing or superficial cell population. All cases were analyzed cytologically by review of the Papanicolaou smear taken at the colposcopic examination and biopsy and without knowledge of the histologic diagnosis. Analysis was conducted with two investigators producing separate panels of diagnosis. All biopsy specimens were analyzed for HPV -DNA. Diagnostic agreement between reviewers was determined by the kappa statistic.
Findings: The reviewers agreed on cytology and histology in 79 and 88% of the cases, respectively. In 75% of cases, both reviewers agreed that a diagnostic cytological and histologic abnormality was present. Overall, reviewers 1 and 2 identified a cytological and histologic abnormality in 64 and 58 cases, respectively. The sensitivities (0.79 and 0.66=, specificities (0.82 and 0.80=, and positive predictive values (0.95 and 0.97) were good to excellent and were similar for reviewers 1 and 2, respectively. In contrast, the negative predictive values (i.e., of low-grade cytology for low-grade histology) were poor for both (0.45 and 0.49, respectively). A strong correlation was observed between histologic diagnosis and HPV type, reflecting primarily the strong association between HPV 16/18 and high grade. In contrast, the correlation between cytology and HPV type was not significant (p=.92=, reflecting the overall lack of correlation between a low-grade Papanicolaou smear and either a low-grade lesion or the absence of high-risk HPV types.
Characteristics of trials identified
Eight randomized or quasi randomized trials were identified. Four of those studies (Matsuura, Mayeux, Soost and Tabbara) were evaluating cytology test per se, having the histopathological exam as a gold standard, all taking the specimens through punch biopsies during colposcopic exam but one, (Matsuura that plus the punch biopsy also studied the cones which were done in all samples that had HGSIL detected in punch biopsies.
The others were comparing slide preparation techniques with the conventional one (Bishop) or comparing different screening tests (Duggan-HPV-DNA; Raid and Schneider - cervicography and HPV-DNA).
There has been used in these studies different collecting devices for conventional cytology Pap smear taking such as, Cervex Brush (Bioshop), Cervex Brush and Ayre spatula (Reid), Swabbing (Matsuura, Mayeux) and Swabbing plus Cervex Brush for stenotic Os (Schneider). Two trials have not pointed out which was the technique used for collecting the smears (Soost and Tabbara).
All trials but two (Soost and Tabbara have done a retrospective study) were conducted as a clinical prospective study.
The samples were taken from primary screening tests by Bishop, Matsuura, Reid Schneider and Soost, but Reid has taken half of the subjects from a high risk group (STD clinic), and Schneider`s subjects were pregnant women. Duggan, Mayeux and Tabbara have chosen already cytological SIL or abnormal (two consecutive inflammatory results after treatment) diagnosis from patients who were sent for colposcopy and punch biopsy.
Statistical analysis were conducted as follows: Duggan used x2 tests to compare subjects risk statues, Willcoxon to compare age and multiple logistic regression to analyze the influence of different variables. Bishop used K statistic technique to evaluate agreement between the screening test; Matsuura used the two-by-two table approach to determine sensitivity, specificity and predictive values; Mayeux mentioned having treated data through Microsoft Excel Version 4 and SAS Version 6.04; Reid used computerized data base and cross checked for accuracy and analyzed with BMDP-88 statistical package within and IBM 386 -2 microcomputer. Besides that standard statistical differences were analyzed by x2 test; Schneider used x2 testing or Fisher’s exact test; Soost studied the data on the two-by-two table to determine predictive value and than estimated sensitivity and specificity of the Cytological tests; finally, Tabbara used the K statistic method to compare diagnostic agreement between tests and cytological and histological results through the x2 statistical technique.
According to the selected studies which were included in this bibliographic review, Pap smear efficacy can be quoted through the following sensitivity and specificity rates:
(*) not specified
Those data are referred to the detection of Squamous Intraepithelial Lesions and invasive cancer of cervix as a whole, with the exception already being mentioned.
The studies included in this bibliographic review show sensitivity rates for Pap smear which ranges from 29% to 80%. These large discrepancies lead to the assumption that Pap smear has not been properly tested. As a matter of fact due to the great impact that a cancer detection screening gives in discovering still symptomatic stages of the disease, no efforts has been done to evaluate the efficacy of Cytology as a cervical screening test as a preventive measure. The best result seen on the trials being reported here were in the detection of high grade squamous intraepithelial lesions - HGIL (moderate dysplasia/microcarcinoma), showing poor results in detecting low grade squamous intraepithelial lesions - LGSIL (mild dysplasias). Indeed it was not also good in detecting frankly invasive cervical neoplasias.
The studies which are being addressed in this paper do not evaluate cytology test per se but compare its result with other screening tests (HPV-DNA and cervicography) using different slide preparation techniques that may have brought confounding variables due to different hazardous conditions influencing their own sensitivity and specificity.
Different target groups with different prevalence of the disease also may have lead to the wide range of sensitivity rate of Pap smear test.
There was quite a consensus in the inclusion of endocervical cells in the smear as a major issue of improving sensitivity though one of the trials (Duggan et al, 1997) has not shown any difference comparing the results where those cells were not included with the ones where they were present in the sample to be studied.
In spite of the discrepancies that have already been discussed on can see the overall sensitivity rates can hardly reach a medium rate of 60.0% (29.0% to 80.0%) among the included studies in this bibliographic review.
The purpose of Pap smear test is to screen for intraepithelial lesions before they progress to invasive disease. Patients have come to expect the Pap test to have 100% sensitivity which means that a false-negative result is for sure somebody made a mistake. Many women and also many clinicians do not realize that Pap smear is just a screening test and is subjected to limitations. It reduces the incidence of cervical cancer but it is not expected to detect all the precursor lesions and it is no appropriated to detect large invasive neoplasias.
Nowadays the best methods for health promotion and recruitment for cervical cancer detection screening are still being investigated. Systematic follow-up, appropriate collect smear devices which allow the collection of endocervical cells and or metaplasic ones, and the targeted screening of women never tested has been considered as main strategies to reduce the number of invasive cases.
Finally, nevertheless the apparent simplicity in detection of cervical intraepithelial neoplasias and cancer of the cervix, numerous epidemiological, biochemical, cytological and socio-economic factors are involved on the efficiency of cytology as a screening test. The challenge is to enhance it with high cost-effective approaches.
Dr. Saloney Nazeer
Characteristics of excluded studies
The above studies were excluded for one of the following reasons: number of subjects or outcomes not clearly stated, and finally, some of those studies were not directly related to the evaluation of Pap smear effectiveness.
References to studies included in this review
Edited by Aldo Campana,