Incidence of female breast cancer in relation to prevalence of risk factors in Denmark

Breast cancer incidence by estrogen receptor status in Denmark from 1996 to 2007

During the past 50 years, breast cancer incidence has increased by 2-3 % annually. Despite many years of testing for estrogen receptors (ER), evidence is scarce on breast cancer incidence by ER status. The aim of this paper was to investigate the increase in breast cancer incidence by ER status. Data were obtained from the clinical database of the Danish Breast Cancer Cooperative Group which holds nationwide data on diagnosis, including pathology, treatment, and follow-up on primary breast cancers since 1977. All Danish women <80 years diagnosed with primary breast cancer 1996-2007 were identified in this prospective register based study. ER status was evaluated using immunohistochemical staining by standardized laboratory methods in the Danish Pathology Departments and reported to the database. From 1996 to 2007, breast cancer incidence increased overall with a tendency to level off after 2002. In all women a significant decrease was found in ER unknown tumors. However, in both pre- and postmenopausal women, significant increases were seen in incidence of ER+ tumors; though the increase levelled off for premenopausal women after 2002. In postmenopausal women, the incidence of ER- breast cancer decreased significantly throughout the period. In women <35 years, we found a minor non-significant increase in both ER+ and ER- tumors. ER unknown decreased in all women and was the most distinct in premenopausal women aged 35+. We found a significant increase in ER+ breast cancer incidence in postmenopausal women whereas the incidence in premenopausal women (aged 35+) levelled off after 2002.

Pregnancy after treatment of breast cancer--a population-based study on behalf of Danish Breast Cancer Cooperative Group

BACKGROUND

Estrogen is an established growth factor in breast cancer and it has been hypothesized that pregnancy associated estrogens may increase the risk of recurrence of breast cancer. In 1997 we published a population-based Danish study indicating no negative prognostic effect of pregnancy after breast cancer treatment. The present study is a ten-year update.

MATERIAL AND METHODS

Danish Breast Cancer Cooperative Group has since 1977 collected population-based data on tumour characteristics, treatment regimes, and follow-up status on Danish women with breast cancer. Pregnancy history was added from the Danish Civil Registration System, the National Birth Registry, and the National Induced Abortion registry. Cox regression was used to estimate the risk ratio of dying among women with a pregnancy after breast cancer treatment compared with women without such experience.

RESULTS

In all, 10 236 women with primary breast cancer aged 45 years or less at the time of diagnosis were followed for 95 616 person years. Among these, 371 women experienced pregnancy after treatment of breast cancer. In a multivariate analysis that included age at diagnosis, stage of disease, and pregnancy history prior to diagnosis, women who had a full-term pregnancy subsequent to breast cancer treatment were found to have a reduced risk of dying (relative risk: 0.73; 95% confidence interval: 0.54-0.99) compared with other women with breast cancer. The effect was not significantly modified by age at diagnosis, tumour size, nodal status, or pregnancy history before diagnosis of breast cancer. Neither spontaneous abortions nor induced abortions subsequent to breast cancer treatment had a negative impact on prognosis.

CONCLUSION

In line with our previous study, but based on more than twice the patient material, we found no evidence that a pregnancy after treatment of breast cancer has a negative influence the prognosis.

Avoiding bias from aggregate measures of exposure

BACKGROUND

Sometimes in descriptive epidemiology or in the evaluation of a health intervention policy change, proportions exposed to a risk factor or to an intervention are used as explanatory variables in log-linear regressions for disease incidence or mortality.

AIM

To demonstrate how estimates from such models can be substantially inaccurate as estimates of the effect of the risk factor or intervention at individual level. To show how the individual level effect can be correctly estimated by excess relative risk models.

METHODS

The problem and solution are demonstrated using data on prostate-specific antigen testing and prostate cancer incidence.

[Time trend of breast cancer incidence in Catalonia]

BACKGROUND AND OBJECTIVE

Time trend of breast cancer incidence in Catalonia in the last 20 years is evaluated by a age-period-cohort model.

POPULATION AND METHOD

Women older than 25 years diagnosed with breast cancer between 1980 and 1999 in the population covered by Tarragona and Girona population-based cancer registries. To investigate the age, period and birth cohort effect in the time trends of breast cancer incidence, Decarli and La Vecchia and Holdford's methods were used.

RESULTS

The world age-standardized rate (25 to > or = 85 years old) has increased from 53.9 cases per 100,000 women-year in the period 1980-1984 to 83.9 per 100,000 women-year in the period 1995-1999. The annual percentage change was 2.2% (95% confidence interval, 1.8-2.6). According to age-period-cohort model an increment of the incidence exists depending on age and birth cohort, being the period effect less important.

CONCLUSIONS

Breast cancer incidence has significantly increased in Catalonia. The birth cohort seems to be more important than the period effect in this increment, which supposes a change on the prevalence of the risk factor, although the use of screening diagnosis techniques might explain a part of the period effect.

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.

The increase of female breast cancer incidence in Japan: emergence of birth cohort effect

During recent decades, breast cancer incidence has been increasing in Japan. According to the latest reports from several cancer registries in Japan, the breast has become the leading cancer site in female cancer incidence. To analyze the trend of breast cancer incidence in detail, we summarized female breast cancer incidence in Miyagi Prefecture, Japan during 1959-1997, and evaluated the period and cohort effect on breast cancer incidence using the age-period-cohort model. Age-specific and age-standardized rates have increased over successive calendar periods. Around 1980, an accelerated increase in these incidence rates took place. A full model including age, period and cohort was best fitted to the trend of incidence. In the model, the effects of period and cohort were statistically significant. The nonlinear effect for cohort indicates an increasing trend, beginning with the cohort in 1888-1897, and the nonlinear effect for period showed a clear increase in risk with calendar period. Furthermore, the full model including a linear component showed a steadily upward trend in the cohort effect. Based on our own epidemiologic studies previously conducted in Miyagi Prefecture, and other published reports, the cohort effect is likely to be related to the change in prevalence of women with risk factors such as low parity and insufficient breastfeeding. We believe that the emergence of the cohort effect is an important finding, although the period effect may also persist. The significant cohort effect may give a caution for continuous increase of breast cancer incidence in Japan.

Breast cancer incidence rates in Slovenia 1971-1993

BACKGROUND

Analyses of time trends in breast cancer incidence and mortality have generally revealed cohort-based changes in the rates. These have been linked to cohort-based changes in lifestyle factors. The effect of the changes in the reproductive risk factors on the changes in the rates, and the relative importance of the reproductive characteristics in Slovenia, a country which has not had much breast cancer screening, are investigated.

METHODS

Data on breast cancer incidence for 1971-1993 were obtained from the Cancer Registry of Slovenia (Registry). The Registry covers the whole population of the Republic of Slovenia (1.99 million on 30 June 1993). The statistical analysis uses parametric age-period-cohort models.

RESULTS

Breast cancer incidence has increased by 70% in Slovenia from 1971 to 1993, These changes are dominated by cohort effects and the cohorts born in 1907-1922 have the greatest increase in incidence. Period effects on changes in incidence were modest. The percentage of nulliparous women in the cohort and the average family size in the cohort explained 38% of the variation in the cohort effects.

CONCLUSIONS

The percentage of nulliparous women in the cohort is the most important reproductive variable associated with the trends in the rates, with breast cancer risk predicted to be higher in cohorts with a larger percentage of nulliparous women. As the cohorts born 1932-1946 have a more favourable reproductive pattern as regards breast cancer risk, compared to the 1907-1922 cohorts, age-specific incidence rates in Slovenia would be predicted to decline in the future in the absence of changes in the other risk factors.

Epidemiology of cancer: global patterns and trends

This paper presents recent estimates of the global cancer burden, in terms of the number of new cancer cases, and incidence rates, ignoring other measures such as mortality, prevalence and years of life lost. For four major cancers, information on temporal trends is reviewed, at least for those parts of the world where adequate data are available. Finally, there is a brief examination of the factors underlying the geographic patterns and trends, with an attempt at quantitation, and some forecasting of the likely evolution of the cancer burden at the global level.

Breast cancer: aetiological factors and associations (a possible protective role of phytoestrogens)

BACKGROUND

In spite of many known and suspected factors associated with the risk of breast cancer there has until recently been no explanation for its continuing increase in women of Western societies over recent decades or why there has not been an equivalent increase in women of most Asian and other less Westernized societies. It has long been suspected that a significant factor has been an increasing change of diet in Western societies from one predominantly vegetarian to one with a high content of meat and dairy products as well as 'refined' foods. Although diet has long been suspected there has otherwise been no real explanation as to the mechanism of the change in incidence of breast cancer.

METHODS

A comprehensive literature review has been made of aetiological factors and associations concerning breast cancer to determine whether any consistent trend can explain the rising incidence in Western societies.

RESULTS

There are a number of likely contributory factors but there is now accumulating evidence that the single most important difference is that people having a vegetarian diet have a high intake of legumes and other plant foods containing a variety of lignans and isoflavonoids. These appear to have an important role as nature's sex hormone modulators. These agents appear to be biologically active in a number of ways not yet completely understood but they do have both a weak oestrogenic effect and an anti-oestrogenic competitive effect, thus reducing the potential carcinogenic action of prolonged oestrogen activity. A probable additional benefit of such diets could be the role of dietary fibre.

CONCLUSIONS

A major problem of Western diets may not be the presence of meat or dairy products in the diet but the absence of desirable ingredients of vegetarian diets, namely dietary fibre and certain plant lignans and isoflavonoids. A modification of diet to include a greater proportion of fibre and soy or other leguminous plant food should be studied. Alternatively addition of more fibre and lignans and especially isoflavonoids to traditional Western diets would seem worthy of serious investigation. Such influences appear to have their greatest impact early in life and therefore could be especially important for girls and young women in Western societies.

Trends in the incidence of female breast and cervical cancers in Miyagi Prefecture, Japan, 1959-1987

Trends in the incidence of female breast and cervical cancers were examined, using the cancer registry data in Miyagi Prefecture, Japan, during 1959-1987. The age-standardized incidence rate of breast cancer has been increasing, while that of cervical cancer has been decreasing. Age-period-cohort models were applied to clarify the trends in incidence. For breast cancer incidence, the age-period model adequately represented the data, and demonstrated that the risk of developing breast cancer has been increasing in recent time periods. The effect of cohort on breast cancer incidence was insignificant and the full model containing age, period and cohort showed irregularities in the cohort effect. For cervical cancer incidence, the effect of period was significant, while the effect of cohort was marginal. The full model containing age, period and cohort showed that cervical cancer risk has been decreasing in recent time periods and younger birth cohorts. Using published reports, we investigated the trends in the prevalence of various risk factors and compared them with the trends in the incidence at both sites. It is suggested that the effects of period and cohort might be related to the changes in the prevalence of these risk factors as well as to improvements of the diagnostic procedures.