A case-control study of the effectiveness of cervical cancer screening in Osaka, Japan

Exposure Definition in Case-Control Studies of Cervical Cancer Screening: A Systematic Literature Review

The first step in evaluating the effectiveness of cervical screening is defining exposure to screening. Our aim was to describe the spectrum of screening exposure definitions used in studies of the effectiveness of cervical screening. This systematic review included case-control studies in a population-based screening setting. Outcome was incidence of cervical cancer. Three electronic databases were searched from January 1, 2012 to December 6, 2018. Articles prior to 2012 were identified from a previous review. The qualitative synthesis focused on describing screening exposure definitions reported in the literature and the methodologic differences that could have an impact on the association between screening and cervical cancer. Forty-one case-control studies were included. Six screening exposure definitions were identified. Cervical cancer risk on average decreased by 66% when screening exposure was defined as ever tested, by 77% by time since last negative test, and by 79% after two or more previous tests. Methodologic differences included composition of the reference group and whether diagnostic and/or symptomatic tests were excluded from the analysis. Consensus guidelines to standardize exposure definitions are needed to ensure evaluations of cervical cancer screening can accurately measure the impact of transitioning from cytology to human papillomavirus-based screening and to allow comparisons between programs.

Performance of papanicolaou testing and detection of cervical carcinoma in situ in participants of organized cervical cancer screening in South Korea

Background

The present study measured the performance of the Papanicolaou (Pap) test and detection of cervical carcinoma in situ (CIS) and cancer in participants of organized cervical cancer screening in South Korea, and examined differences in the proportion of CIS according to socio-demographic factors.

Methods

Data were obtained from the National Cancer Screening Program and National Health Insurance Cancer Screening Program databases. We analyzed data from 4,072,997 screenings of women aged 30 years or older who underwent cervical cancer screening by Pap test between January 1, 2005 and December 31, 2006. We calculated the performances of the Pap test and compared that according to socio-demographic factors.

Results

The positivity rate for all screenings was 6.6%. The cancer detection rate (CDR) and interval cancer rate (ICR) were 0.32 per 1,000 screenings, and 0.13 per 1,000 negative screenings, respectively. About 63.4% of screen-detected CIS+ cases (CIS or invasive cervical cancer) were CIS. The CDR and ICR, and percentage of CIS among all CIS+ were significantly different by age group and health insurance status. The odds ratios of CDR and ICR were higher for Medical Aid Program (MAP) recipients compared with National Health Insurance (NHI) beneficiaries. The likelihood of a detected CIS+ case to be CIS was significantly lower among MAP recipients than among NHI beneficiaries.

Conclusions

The difference in performance of cervical cancer screening among different socio-demographic groups may indicate an important influence of socio-demographic factors on preventive behavior. The findings of the study support the critical need for increasing efforts to raise awareness and provide more screening in at-risk populations, specifically low-income groups.

Effectiveness of cervical cancer screening over cervical cancer mortality among Japanese women

BACKGROUND

Various studies have revealed that cervical cancer (CC) screening significantly reduces both CC incidence and mortality in developed countries. Although Japan introduced a nationwide government funded annual CC screening for the women aged 30+ in 1982, the effectiveness of CC screening on CC mortality has not yet been evaluated by any prospective cohort study. Therefore, the present study evaluated the association of CC mortality with self-reported CC screening and some other factors by a nationwide cohort study.

METHODS

Baseline survey of the Japan Collaborative Cohort Study for the enrollment of subjects was completed during 1988-90 and followed until 2003. This study only analyzed 63,541 women, aged 30-79 years, who were free from any cancer history at enrollment.

RESULTS

During the follow-up period, 38 CC deaths were identified. The mean age at mortality was 67.0 years, with a mortality rate of 4.2 per 100,000 person-years. Participation rate in CC screening was 46.9%. Age-adjusted Cox model indicated significantly lower CC mortality [hazard ratio (HR) = 0.30, 95% confidence interval (CI) = 0.12-0.74] due to CC screening. Protectiveness remained almost the same (HR = 0.30, 95% CI = 0.12-0.76) when adjusted for age, body mass index and number of deliveries. The results also revealed that CC screening could reduce at least 50% of CC deaths even after excluding the effect of possible self-selection bias.

CONCLUSIONS

CC screening in Japan may reduce CC mortality significantly for women aged 30-79 years. However, further studies with more CC deaths and increased statistical power are needed to validate the findings.

Confounding by dietary factors in case-control studies on the efficacy of cancer screening in Japan

Evaluation of cancer screening using case-control studies is less valid in comparison to randomized controlled trails, due to the intrusion of a possible self-selection bias in the former. The randomized controlled trial approach, however, may be difficult in developed countries where mass cancer screening programs are already being performed nationally. Accordingly, case-control studies are often performed instead of randomized controlled trials. In case-control studies, no reports could be found in the literature using dietary habit, an important influencing factor in carcinogenesis, as an adjusting item. We surveyed nutrition and food intake status through a nutrition survey using the weighing method, and smoking prevalence and alcohol consumption with questionnaires in the general population in northern Japan, in subjects over 30 years of age. We then compared these results among non-participants and participants in cancer screening programs, and evaluated how any differences between the two groups might affect the results of case-control studies. Non-participants had a significantly lower intake of vegetables, carotene, vitamin C, and dietary fiber, which are thought to be beneficial factors in the prevention of carcinogenesis. Non-participants had a significantly higher cigarette smoking prevalence than participants. In relation to the intake of vegetables, a difference between participants and non-participants was evident, as proper adjustment for vegetable intake led to an odds ratio closer to the null value. The value of the odds ratio will probably not decrease, but it might increase when other dietary factors or smoking are taken into consideration.

Racial and ethnic disparities in cancer screening: the importance of foreign birth as a barrier to care

CONTEXT

Racial/ethnic groups comprised largely of foreign-born individuals have lower rates of cancer screening than white Americans. Little is known about whether these disparities are related primarily to their race/ethnicity or birthplace.

OBJECTIVE

To determine whether foreign birthplace explains some racial/ethnic disparities in cancer screening.

DESIGN, SETTING, AND SUBJECTS

Cross-sectional study using 1998 data from the National Health Interview Survey.

MAIN OUTCOME MEASURES

Completion of cervical, breast, or colorectal cancer screening.

RESULTS

Of respondents, 15% were foreign born. In analyses adjusted for sociodemographic characteristics and illness burden, black respondents were as or more likely to report cancer screening than white respondents; however, Hispanic and Asian-American and Pacific Islander (AAPI) respondents were significantly less likely to report screening for most cancers. When race/ethnicity and birthplace were considered together, U.S.-born Hispanic and AAPI respondents were as likely to report cancer screening as U.S.-born whites; however, foreign-born white (adjusted odds ratio [AOR], 0.58; 95% confidence interval [CI], 0.41 to 0.82), Hispanic (AOR, 0.65; 95% CI, 0.53 to 0.79), and AAPI respondents (AOR, 0.28; 95% CI, 0.19 to 0.39) were less likely than U.S.-born whites to report Pap smears. Foreign-born Hispanic and AAPI respondents were also less likely to report fecal occult blood testing (FOBT); AORs, 0.72; 95% CI, 0.53 to 0.98; and 0.61; 95% CI, 0.39 to 0.96, respectively); and sigmoidoscopy (AORs, 0.70; 95% CI, 0.51 to 0.97; and 0.63; 95% CI, 0.40 to 0.99, respectively). Furthermore, foreign-born AAPI respondents were less likely to report mammography (AOR, 0.49; 95% CI, 0.28 to 0.86). Adjusting for access to care partially attenuated disparities among foreign-born respondents.

CONCLUSION

Foreign birthplace may explain some disparities previously attributed to race or ethnicity, and is an important barrier to cancer screening, even after adjustment for other factors. Increasing access to health care may improve disparities among foreign-born persons to some degree, but further study is needed to understand other barriers to screening among the foreign-born.

Case-control studies of cancer screening: theory and practice

This review summarizes methodologic theories for the design of cancer screening case-control studies and examines the methods applied in studies published in English from 1980 through 1996. In addition to summarizing state-of-the-art methodologic approaches, we identify areas where obvious gaps exist between theory and practice, and we recommend potential areas where theory and methodology may need further development. In particular, we focus on three major areas: 1) the selection of case and control subjects, 2) the definition of exposure (i.e., exposure to the screening test), and 3) bias. Each area is considered carefully by summarizing current theory, reviewing cancer screening applications, and linking recommended methodologic approaches to those used in practice to identify areas where inconsistencies exist. In general, we found methodologic theory and practice in this field of research to be consistent. However, discrepancies were identified in the area of exposure definition, including the use of screening frequency and the use of a detectable, curable preclinical phase for case subjects as the exposure measures. Even when recommended methods were followed, a number of difficulties arose in practice. Specific concerns included the ability to carry out the following: identifying all case subjects within a source population, defining eligibility criteria to ensure that case and control subjects had equal access to screening during the exposure period, distinguishing between symptomatic and diagnostic tests, and controlling for self-selection bias. Careful scrutiny is warranted in all aspects of the design of cancer screening case-control studies, and caution is advised in the interpretation of study results.

The evaluation of screening for gastric cancer in Miyagi Prefecture, Japan: a population-based case-control study

Although a screening program for gastric cancer, using barium X-ray examination, has been carried out widely in Japan for the past 3 decades, there is insufficient evidence to confirm its effectiveness in terms of reducing mortality. To evaluate the effectiveness of the screening, a population-based case-control study was carried out in Miyagi Prefecture, Japan. Case subjects, who had died from gastric cancer (198) and control subjects matched in age, sex and residence (577) were selected from among members of the National Health Insurance. Their screening histories during 5 years before the cases were diagnosed were surveyed on the basis of records of the regional cancer registry and the cancer-detection center. The odds ratio (OR) of death from gastric cancer for the persons who participated in the screening at least once during 5 years was 0.41. For those who participated only once during 5 years the OR was 0.43, and for those whose last participation was 5 years earlier it was 0.30. Our data suggest that screening for gastric cancer at 5-year intervals might reduce mortality by 60%, and that the effect might remain for at least 5 years.

A critical review of cancer screening programs in Japan

In Japan, screening programs for various cancers have been eagerly conducted as part of public health policy. However, these programs have not always produced the results that were originally expected. To improve the ill-planned and unscientific state of the current programs in Japan, two proposals are made.

A study on the efficacy of a screening program for colorectal cancer in a small Japanese village

A longitudinal study of the reduction in mortality was carried out to evaluate the efficacy of screening for colorectal cancer. A population-based screening program using the fecal occult blood test was conducted from 1982 to 1991 in the small village of Asahi, Nagano, Japan (index area). The efficacy of the screening program was measured by the standardized mortality ratio (SMR) for colorectal cancer. The SMR in the index area was 150 before screening (1972-1981) and 54 during screening (1982-1991). In addition to a significantly lower SMR in the latter period (P < 0.01), the change in the relative incidence--(D-B)/B, where D is the SMR during screening, and B is the SMR before screening--showed a 64% reduction. The SMR in Asahi was also compared with that in four neighboring villages (control area) not covered by the screening. The SMR in the control area was 133 before and 121 during screening, for a (D-B)/B value of -9%. The reduction in the relative incidence of colorectal cancer was thus significantly higher in the index area than in the control area (P < 0.01). These results confirm that the screening program conducted in the index area was effective as a preventive community measure in reducing mortality from colorectal cancer, and that the time trend assessment employed here is a useful method for evaluating the efficacy of cancer screening.

An evaluation of mass screening using fecal occult blood test for colorectal cancer in Japan: a case-control study

There is as yet no firm evidence showing that mass screening for colorectal cancer using fecal occult blood tests (FOBTs) reduces the mortality from this cancer. Therefore we evaluated the effectiveness of the screening by a case-control study in Miyagi Prefecture, Japan. The study included as case subjects 28 individuals who had died from colorectal cancer and had had an opportunity to participate in the mass screening before the date of diagnosis as colorectal cancer, and 3 controls for each case subject randomly selected from residents who were alive on the date of death of case subjects and matched by sex, age (within 3 years) and living area using residential files. For each set, i.e., a case subject and 3 controls, screening histories before the date of the diagnosis of the case as colorectal cancer were examined. Both the case subjects and the controls who had participated in the screening at least once within 3 years before the date of diagnosis of the case were classified as "screened." The 28 case subjects consisted of 12 males and 16 females (average age: 60.8 years). The odds ratio of death from colorectal cancer for the screened versus the non-screened persons was 0.24 (95% confidence interval = 0.08-0.76) by the Mantel-Haenszel method. The present study suggests that mass screening using FOBTs for colorectal cancer significantly reduces the mortality from this cancer epidemiologically.

Large-scale, population-based prospective studies in Japan

Large scale, population-based prospective studies have increasing importance for the study of common cancers in view of the possibility of advancing the understanding of different risk factors in the initiation, promotion and progression phases during what is thought to be the long process of human carcinogenesis. The permanent registration system in Japan ("Koseki") simplifies the follow-up of registered participants of such cohorts. The population-based cohort studied by Hirayama and the cohort of the atomic bomb survivors started during the 1960s are examples of such possibilities in Japan. Rapidly changing patterns of disease and lifestyles during the last 30 years require new population-based prospective studies focusing on a different set of exposures and with increased detail of exposure assessment. We have established a new population-based prospective study, the "Koseisho" cohort, between 1990 to 1992, following a cross-sectional study, using various biomarkers in five health centre districts. The Koseisho cohort comprises approximately 170,000 people aged 40-59 or 40-69 in 12 different health centre districts. The data are linked with the mass screening program registry data every year, and the sera and buffy coats collected at the beginning of the study will be stored at -80 degrees C for at least 10 years. We intend to integrate various sources of information about health conditions for the prevention of chronic diseases in these cohort areas. Nutritional practices are one of our main interests, and repeated surveys by different methods are planned. Although all death certificates are collected through the health centres, disease registration committees were established in each district to register incident cases of both cancer and certain cardiovascular diseases. Representative population-based prospective studies in Japan are briefly reviewed and introduced.

The effect of mass screening for breast cancer: results of a multivariate analysis

To evaluate the life-prolonging effect of mass screening for breast cancer, we compared the risk of death for the patients detected by mass screening with that for the patients diagnosed in out-patient clinics, after adjusting for other relevant factors simultaneously by using the Cox regression model. A multivariate analysis using the Cox regression model in which clinical staging of disease was taken as one of the independent variables, showed that the risk of death for patients detected by mass screening was smaller by 0.765 times than that for patients found in out-patient clinics although the reduction was not statistically significant. This small reduction might be partly due to the effect of mass screening through early detection even within the same stage, and partly due to length bias, lead time bias and self-selection bias. When clinical staging of disease was removed from the independent variables, the risk of death for patients detected by mass screening was reduced from 0.765 times to 0.677 times that for patients diagnosed in out-patient clinics, which was statistically significant (P greater than 0.01). For asymptomatic patients detected by mass screening, such as reduction of the risk of death was from 0.789 times to 0.555 times that for patients found in out-patient clinics (P less than 0.05). These results suggest that mass screening for breast cancer may contribute to the reduction of the risk of death, although the effect of biases inherent in periodic screening was not removed completely in the present analysis.