Trends in cervical and breast cancer in Iceland. A statistical evaluation of trends in incidence and mortality for the period 1955-1989, their relation to screening and prediction to the year 2000

Prediction of cervical cancer incidence in England, UK, up to 2040, under four scenarios: a modelling study

BACKGROUND

In the next 25 years, the epidemiology of cervical cancer in England, UK, will change: human papillomavirus (HPV) screening will be the primary test for cervical cancer. Additionally, the proportion of women screened regularly is decreasing and women who received the HPV vaccine are due to attend screening for the first time. Therefore, we aimed to estimate how vaccination against HPV, changes to the screening test, and falling screening coverage will affect cervical cancer incidence in England up to 2040.

METHODS

We did a data modelling study that combined results from population modelling of incidence trends, observable data from the individual level with use of a generalised linear model, and microsimulation of unobservable disease states. We estimated age-specific absolute risks of cervical cancer in the absence of screening (derived from individual level data). We used an age period cohort model to estimate birth cohort effects. We multiplied the absolute risks by the age cohort effects to provide absolute risks of cervical cancer for unscreened women in different birth cohorts. We obtained relative risks (RRs) of cervical cancer by screening history (never screened, regularly screened, or lapsed attender) using data from a population-based case-control study for unvaccinated women, and using a microsimulation model for vaccinated women. RRs of primary HPV screening were relative to cytology. We used the proportion of women in each 5-year age group (25-29 years to 75-79 years) and 5-year period (2016-20 to 2036-40) who have a combination of screening and vaccination history, and weighted to estimate the population incidence. The primary outcome was the number of cases and rates per 100 000 women under four scenarios: no changes to current screening coverage or vaccine uptake and HPV primary testing from 2019 (status quo), changing the year in which HPV primary testing is introduced, introduction of the nine-valent vaccine, and changes to cervical screening coverage.

FINDINGS

The status quo scenario estimated that the peak age of cancer diagnosis will shift from the ages of 25-29 years in 2011-15 to 55-59 years in 2036-40. Unvaccinated women born between 1975 and 1990 were predicted to have a relatively high risk of cervical cancer throughout their lives. Introduction of primary HPV screening from 2019 could reduce age-standardised rates of cervical cancer at ages 25-64 years by 19%, from 15·1 in 2016 to 12·2 per 100 000 women as soon as 2028. Vaccination against HPV types 16 and 18 (HPV 16/18) could see cervical cancer rates in women aged 25-29 years decrease by 55% (from 20·9 in 2011-15 to 9·5 per 100 000 women by 2036-40), and introduction of nine-valent vaccination from 2019 compared with continuing vaccination against HPV 16/18 will reduce rates by a further 36% (from 9·5 to 6·1 per 100 000 women) by 2036-40. Women born before 1991 will not benefit directly from vaccination; therefore, despite vaccination and primary HPV screening with current screening coverage, European age-standardised rates of cervical cancer at ages 25-79 years will decrease by only 10% (from 12·8 in 2011-15 to 11·5 per 100 000 women in 2036-40). If screening coverage fell to 50%, European age-standardised rates could increase by 27% (from 12·8 to 16·3 per 100 000 by 2036-40).

INTERPRETATION

Going forward, focus should be placed on scenarios that offer less intensive screening for vaccinated women and more on increasing coverage and incorporation of new technologies to enhance current cervical screening among unvaccinated women.

FUNDING

Jo's Cervical Cancer Trust and Cancer Research UK.

The influence of mammographic screening on national trends in breast cancer incidence

Introducing an organized mammographic screening programme affects the breast cancer incidence rate in a population. The diagnosis is advanced in time, and initially, an increase will occur in the number of cases, followed by a drop in the rate when women leave the programme. The aim of this study was to quantify the potential effects that mammographic screening programmes have on breast cancer incidence. In addition, we wanted to investigate how the incidence of breast cancer varies between different birth cohorts, age groups and time periods in the five Nordic countries Finland, Denmark, Iceland, Norway and Sweden, adjusting for the effects of the screening programmes. Time trends were analysed over the period 1978-1997, using age-period-cohort models. In Sweden, the rates more than doubled (relative risk (RR)=2.20, 95% confidence interval (CI) 1.8-2.6) in women offered screening for the first time compared with women not offered screening. The risk remained elevated (RR=1.34, 95% CI 1.2-1.6) for women who were continued to be offered screening, compared with women who were not offered screening. Finally, the rates dropped (RR=0.68, 95% CI 0.6-0.8) when the women left the programme. This indicates that screening advances the time of diagnosis, which is a prerequisite to subsequent reduction in mortality. Analysis of secular trends, corrected for the influence of screening, showed that the rates in Finland increased by 13% per 5-year period, with a more modest increase in the other countries. There were strong cohort effects in all Nordic countries, and the risk seemed to be flattening for the youngest cohorts in most of the countries.

Effects of screening on cervical cancer incidence and mortality in New South Wales implied by influences of period of diagnosis and birth cohort

STUDY OBJECTIVES

Cervical cancer incidence and mortality in NSW during 1972-1996 is examined under counterfactual assumptions to estimate the number of new cervical cancer cases averted and deaths avoided, with projections to 2006.

SETTING

Cervical cancer incident cases and deaths in NSW for 1972-96 were obtained from the NSW Central Cancer Registry, Sydney, Australia.

DESIGN

Data were analysed by age-period-cohort (APC) modelling, using Poisson regression. Projection of incidence to 2006 was based on a linear trend for period effects. A counterfactual scenario was constructed assuming stable period effects (1972-74), but modelled cohort effects. Modelled rates were converted to cases and deaths (using mortality:incidence ratios for cervical cancer), and compared with actual data to estimate cancers prevented and deaths averted due to screening.

RESULTS

Rising cohort effects with recency of birth were found after controlling for age and period of diagnosis, and declining period effects were identified after controlling for age and birth cohort. The estimated cumulated number of new cases of cervical cancer prevented during 1972-1996 was 3440. The cumulated number of averted deaths over 1972-1996, derived from incident cases, was estimated to be 1610 (including actual declines in the M/I ratio). With no change in the M/I ratio from 1972, estimated cumulated mortality averted due to cervical cancer for 1972-1996 was 1210 deaths.

CONCLUSIONS

Cervical screening has prevented a substantial number of new cases of cervical cancer and deaths. In addition, secondary prevention and improved treatment has contributed further to cervical cancer deaths averted.

Associations between community income and cancer incidence in Canada and the United States

BACKGROUND

Associations between socioeconomic status (SES) and the incidence of cancer have been reported previously in the U.S. Canada has more comprehensive health care and social programs than the U.S. The purpose of this study was to compare the strength of associations between SES and cancer incidence in Canada and the U.S.

METHODS

The regions studied were the Canadian province of Ontario and the areas of the U.S. covered by the Surveillance, Epidemiology, and End Results (SEER) program. The populations at risk were defined using the 1991 Canadian Census and the 1990 U.S. Census. The populations of Ontario and of the SEER areas of the U.S. were each divided into deciles on the basis of median household income. Population-based cancer registries were used to identify incident cases. Age-standardized incidence rates for all major groups of malignant diseases were calculated for each SES decile in Ontario and in the U.S. Income-associated incidence gradients observed in Ontario and the U.S. were compared.

RESULTS

The incidence of most types of cancer was similar in Ontario and the U.S. In both countries, there were moderately strong, inverse associations between income level and the incidence of carcinomas of the cervix, the head and neck region, the lung, and the gastrointestinal tract. In both Ontario and the U.S., several of these diseases were twice as common in the bottom income decile than they were in the top decile. In contrast, carcinoma of the female breast and carcinoma of the prostate were more common among higher income communities in both countries, but the observed associations were weaker in Ontario.

CONCLUSIONS

Despite Canada's universal health insurance and more comprehensive social security system, the association between lower socioeconomic status and the incidence of many common cancers is just as strong in Ontario as it is in the U.S. The mechanisms responsible for these associations require further investigation.

Breast cancer in Norway 1970-1993: a population-based study on incidence, mortality and survival

The incidence, mortality and survival of breast cancer patients from 1970 to 1993 were studied using data from the Cancer Registry of Norway. The age-adjusted incidence rate increased from 62.0 to 76.9 per 100,000 person-years during the period, and more than 2000 cases are now registered annually. The increase tends to be highest in the age group below 40 years. The increase is mainly found in cases with localized tumours at the time of diagnosis. The mortality rate has been almost unchanged in the period; the age adjusted mortality rate is 27.0 per 100,000 person-years at the end of the study period. The 5-year overall survival has increased among cases with axillary lymph node metastases at the time of diagnosis; the other stages show only little improvement.

Efficiency of cytological screening for detection of cervical squamous carcinoma. A study in the county of Uppsala 1991-1994

Squamous carcinoma of the uterine cervix accounts for a considerable mortality among gynecological malignancies, although both the incidence of and mortality from cervical cancer have decreased in the Nordic countries since 1970. The reduction is a result of the cytologic screening program, through which precursor lesions can be detected and removed. Our aim was to determine why women in the county of Uppsala get cervical cancer despite extensive gynecological screening. A retrospective study of all women (43 cases) who developed histologically verified cervical squamous carcinoma in the county of Uppsala during the years 1991 to 1994 was undertaken. A central computer database covering all histopathological and cytological material made it possible to compare each woman's previous smears or lack of smears with her cancer diagnosis. Twenty women (47%, mean age at diagnosis 64.4 years) had not undergone cytological screening. Twenty-three women (53%) had been screened at least once within 6 years before tumor diagnosis. Of these, 11 (mean age 47.5 years) had had normal smears for the last 6 years, 8 (mean age 44.3 years) had shown abnormal cytology for less than one year and 4 (mean age 39.0 years) had shown abnormal cytology for more than one year and up to 6 years before their cervical cancer diagnosis. Women with cervical squamous carcinoma, who are not covered by the gynecological screening program (47%) are at increased risk of developing cervical cancer compared with other women. Consequently the average age of non-screened women developing cancer is considerably higher (64.4 years) than that of women with cancer screened previously (44.9 years). In 26% of the total group of women with cervical squamous carcinoma previous cytology displayed normal features.

What attendance rate can be achieved for Pap smear screening? A case-control study of the characteristics of non-attenders and results of reminder efforts

OBJECTIVE

To understand participation failures in a national Pap smear screening programme by studying characteristics of non-attenders and results of further reminder efforts.

DESIGN

A case-control and an intervention study.

SETTING

The community health centre in the town of Hafnarfjördur, Iceland.

SUBJECTS

The target population comprised 2510 women aged 35-69, who were invited regularly every second year for cervical cancer screening.

MAIN RESULTS

2241 (89.3%) had attended screening during the preceding five years, 102 (4.1%) had never attended, and 167 (6.7%) had attended previously but not during the preceding five years. Women with a mental disorder and those who had never married were more likely not to attend. The most usual explanations given by non-attenders were that they did not like to participate, or they felt they did not need to, some of them because their uterus had been removed. Of the non-attenders 29 (10.8%) came for a Pap smear after repeated reminding efforts.

CONCLUSIONS

Total participation rate in cervical cancer screening programmes in Iceland is high. When efforts are taken to lower the non-attendance rate it has to be kept in mind that many women are unwilling or unable to participate in such preventive measures.

Detection rates for abnormal cervical smears: what are we screening for?

We analysed rates of detection for smear abnormalities in 255,000 women served by the Bristol screening programme. The programme began in 1966 with the aim of eradicating the 30-40 deaths each year in Bristol from cervical cancer. Organisation has been good and population uptake has been high for the past 15 years. Records were computerised in 1977. During the 1988 to 1993 screening round, 225,974 women were tested. New smear abnormalities were found in 15,551, of whom nearly 6000 were referred for colposcopy. These numbers are excessively high in comparison with the incidence of the malignancy we are trying to prevent. The effect of screening on death rates in Bristol is too small to detect. Our conclusion is that despite good organisation of the service, much of our effort in Bristol is devoted to limiting the harm done to healthy women and to protecting our staff from litigation as cases of serious disease continue to occur. The real lesson from 30 years' cervical screening is that no matter how obvious the predicted benefit may seem for any screening test, introduction should never take place without adequate prior evaluation of both positive and negative effects in controlled trials.

Quality assurance in cervical cancer screening: the Icelandic experience 1964-1993

Monitoring of the effectiveness of a screening programme is vital to ensure optimal use of public resources. This report correlates the results of the Icelandic cervical cancer screening programme with the results of monitoring the programme since 1964. Screening has significantly decreased both the incidence and mortality rates and greatly affected the stage distribution of squamous cell carcinomas, but not of adeno- and adenosquamous carcinomas. In the 25-64 years age group, 84% were screened, 80% of whom were in the organised screening. Smears taken outside the guidelines amounted to 10%. Sensitivity at 1 year was 93% for all smears. At 3 years it was 81% for squamous cell carcinomas, and 42% for adeno-and adenosquamous carcinomas. The rate of unsatisfactory smears was 1.3% for all smears, and 4.5% of the women had abnormal smears (7.7% in the 20-24 years age group). The specificity of the smears test was 98%. It is concluded that monitoring is vital for optimal screening results and although screening is effective in the targeted age group of 25-64 years it should preferably start sooner after age 20 years with a screening interval of 2-3 years.

Effect of organized screening on the risk of cervical cancer. Evaluation of screening activity in Iceland, 1964-1991

The Icelandic Cancer Society launched a screening programme for cervical cancer in June 1964. The aim was to lower the incidence and mortality rates by screening the age group 25-69 at 2- to 3-year intervals. This report analyses the trends in invasive and pre-invasive disease and the distribution of stage and histology, and also evaluates the attendance, the target age group and the screening interval. Before screening, the incidence and mortality rates were on the increase but both have since fallen significantly. Screening greatly affected the rate of microinvasive and stage > or = II squamous-cell carcinomas but not the rate of adeno- and adenosquamous carcinoma. The mean age at detection of invasive cancer has decreased significantly and cancer has become practically non-existent among correctly screened subjects over the age of 69. Among younger women the rates of moderate and severe pre-invasive lesions at first visit increased significantly after 1980. The rate of these lesions was fairly consistently high only 1 year after the first normal visit. It is concluded that organized screening, co-ordinated with spontaneous activity, is effective in reducing the risk of cervical cancer. Regular high attendance and strict follow-up of abnormal cases is a prerequisite for good screening results. Screening should preferably start at about the age of 20 and extend to 60-69 years of age, depending on the number of negative smears by that age. Screening can safely start with a screening interval of 2 to 3 years, but this interval can probably be extended to 4 or 5 years at older ages.

The relationship between age and incidence of breast cancer. Population and screening program data

Despite extensive study of breast cancer incidence, including specific studies of the relationship between age and breast cancer incidence, the picture remains confusing. This article examines not only the relationship between age and breast cancer, but also trends over time related to this relationship to discern the underlying true age-incidence pattern. The age-incidence curve changes around the menopausal period, most likely due to hormonal changes 10 to 15 years earlier, flattens out in the 40 to 50 year old age range, and then increases as age increases. Recent data showing decreased risk of breast cancer incidence at older ages, e.g., older than 75 years of age, relative to younger ages, are likely an artifact of recent increases in breast cancer screening in the United States. This picture is consistent with increases in screening and with notions of lead time created by increased screening. The increase in screening that has changed the age-incidence relationship may eventually deliver benefits to United States women in terms of mortality deficits, but this is not guaranteed unless screening becomes routine practice and high-quality therapeutic intervention and follow-up occurs as well.

Screening as a prognostic factor in cervical cancer: analysis of survival and prognostic factors based on Icelandic population data, 1964-1988

Survival rates were computed for 376 women diagnosed with carcinoma of the uterine cervix between 1964 and 1988. The 5-year survival rate for the entire group was 63%. The effect of age at diagnosis, clinical stage, histopathology, year of diagnosis, and screening program attendance was studied by univariate analysis and simultaneously with a multivariate analysis, the Cox proportional hazards model. All these parameters had a significant effect on survival, with clinical stage as the strongest parameter followed by histology, year of diagnosis, age at diagnosis, and attendance at screening. Women who had attended the cervical screening program fared significantly better than those who had never attended. Patients treated in the late years of the study period had a significantly better survival rate, possibly indicating improved treatment. Young women had a significantly better prognosis than older women. Women with adenocarcinoma and anaplastic tumors had a significantly worse prognosis than women with squamous and adenosquamous carcinoma. The prognostic effect of screening was mainly attributed to the more favorable distribution of early stages and younger age at diagnosis among the screened women. After all the analyzed parameters had been adjusted for the nonattenders still had poorer prognosis.