Elsevier

Gynecologic Oncology

Volume 112, Issue 3, March 2009, Pages 572-576
Gynecologic Oncology

Superior performance of liquid-based versus conventional cytology in a population-based cervical cancer screening program

https://doi.org/10.1016/j.ygyno.2008.12.012Get rights and content

Abstract

Objective

Liquid-based cytology may offer improvements over conventional cytology for cervical cancer screening. The two cytology techniques were compared in a group of 86,469 women who participated in a population-based screening program. Using a nation-wide pathology database containing both cervical cytology and histology records for all patients, we compared the outcome of the two screenings methods with regard to the detection rate of histological proven abnormalities and the determination of the true false-negative rates for both methods.

Methods

Two cohorts of women living in the same geographical region were used. Cohort 1 (n = 51,154 women) was analysed using conventional cytology (conventional cohort) and cohort 2 (liquid cohort) (n = 35,315 women) was analysed using liquid-based cytology (SurePath®). The samples were processed in one laboratory. The results of histological follow up were available via a central database.

Results

The rate of unsatisfactory slides was significantly lower using liquid-based cytology (0.13% vs. 0.89%, p < 0.0001). Detection of ASCUS+ (Atypical squamous cells of unknown significance or higher abnormalities) was significantly higher using liquid-based cytology (2.97% vs. 1.64%, p < 0.0001), mainly due to the increase in the ASCUS category. The percentage of histological abnormalities within the ASCUS samples was approximately equal in both cohorts, indicating that more true abnormal cases were detected using liquid-based cytology. The sensitivity for detection of a histological proven lesion is significantly higher in the liquid cohort compared to the conventional cohort (96.2% vs. 92.0%), with only a slight difference in specificity (97.8% vs. 98.2%).

Conclusion

This population study confirmed previous institution-based reports of decreased numbers of unsatisfactory samples based on liquid-based cytology and showed an increased sensitivity for the detection of cytological abnormalities that was validated by subsequent histological investigation.

Introduction

Worldwide screening programs for cervical cancer based on the Papanicolaou (PAP) smear have contributed to the decrease in incidence and mortality of cervical cancer [1]. Nevertheless, both false-negative and false-positive results due to sampling and screening errors are well-recognized problems. Liquid-based cytology was introduced as an alternative to conventional cytology screening in the hope of improving specimen adequacy and sensitivity in detecting cervical abnormalities. Various studies have shown that liquid-based cytology is more effective in the detection of cervical intraepithelial neoplasia (CIN), reduces the number of unsatisfactory specimens, and reduces screening time compared to conventional cytology [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13].

A nationwide, government-sponsored cervical screening program has been operative in the Netherlands for more than 25 years. All a-symptomatic women between 30 and 60  years of age are invited by the local health authorities to participate in this screening program. At 5-year intervals cervical cytology samples are taken by general practitioners and sent to regional pathology laboratories. In the region of Southwest Holland, 56% of women within the defined population participate in the program [14], [15]. Ninety five percent of the smears are sent to one laboratory. Despite this quality-controlled, well-organised, population-based screening program, the proportion of false negative smears is about 20% [16]. Therefore, we introduced a liquid-based cytology system (SurePath®, BD Diagnostics, Tripath, Burlington, NC 27215 USA) in this region in 1997 to study the effectiveness of this method in comparison with conventional cytology.

We investigated the sensitivity and specificity of these two screening techniques in a group of 86,469 women participating in a population-based screening program. We compared the outcome of the two screening methods with regard to the detection rate of histological abnormalities. The false negative rate was investigated using our nationwide pathology database containing both cervical cytology as well as histology results for all women. By using this database we were able to achieve 100% of follow-up in cases with subsequent biopsies.

Section snippets

Patients and screening methods

This study was conducted in one pathology laboratory in Southwest Holland that screens Pap specimens obtained from approximately 500 general practitioners. The material consisted of samples from asymptomatic 86,469 women (age 30–60) participating in the national screening program, collected during the period July 1997–June 2002. This age window was chosen as a result of the inclusion criteria put forward by the national screening program. The women chosen were a-symptomatic according to the

Patient characteristics

Samples were collected from 86,469 women between the ages of 30 and 60. The study cohorts consisted of 51,154 conventional smears (conventional cohort) and 35,315 liquid-based cytology slides (Cohort 2). There was no difference in age-distribution between the two cohorts (average 43.9 years vs. 43.7 years of age).

Cytology

Cytology results within the two cohorts are shown in Table 1. The percentage of unsatisfactory slides based on liquid-based cytology (Cohort 2) was significantly less compared to

Discussion

A Nation-wide screening program for cervical cancer has been operative in the Netherlands since 1975. Although this program is well controlled and uses skilled cytotechnologists, a false-negative rate of about 20% for HSIL or higher lesions has been observed [16]. Methods to reduce the false–negative rate were investigated including the introduction of liquid-based cytology.

Various studies have reported the advantages of liquid-bases cytology over conventional cytology [2], [13] but

Conflict of interest statement

The authors do not declare any conflict of interest, nor any financial support by SurePath®, TriPath Imaging, Inc., Burlington NC, USA for performing this study.

Acknowledgments

The National Pathology Database PALGA is gratefully acknowledged. This study could not have been performed without the support and enthusiasm of the primary health care physicians within our region, as well as the cooperation from patients.

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