Fertility pattern does not explain social gradient in breast cancer in denmark

Abstract

The present study was undertaken to assess the impact of reproductive behavior on the social class gradient in breast cancer occurrence in Denmark. Objectives were to study whether the gradient across socioeconomic groups could be explained by fertility differences, whether the gradient across educational groups could be explained by fertility differences and whether the effect of socioeconomic group on breast cancer incidence and mortality could be explained by education and vice versa. We studied 674,084 women aged 20 -39 at the census on 9 November 1970 for whom we had complete data on fertility history. The cohort was followed up for breast cancer incidence and mortality until 8 November 1998. Fertility history varied considerably across socioeconomic group, where 38% of the academics were childless at the age of 30, in contrast to only 8% of women in agriculture. The academics had the highest risk of breast cancer and women in agriculture had the lowest risk. For incidence, the gradient in the relative risks was 1.74, which changed to 1.49 when fertility history was incorporated and to 1.29 when school education was also taken into account. For school education, women with > 12 years of schooling had the highest risk and women with < 7 years of schooling had the lowest risk. For incidence, the gradient in the relative risk was 1.38, which changed to 1.26 when fertility history was incorporated and to 1.22 when socioeconomic group was also taken into account. Breast cancer is the most frequent cancer in women in the Western world, now affecting nearly 1 in 10 women, and the incidence is steadily increasing. Recent results confirm that the risk of breast cancer increases with increasing socioeconomic status. 1 The best-established risk factor for breast cancer is late age at first birth and nulliparity. 2 Reproductive behavior is known to vary across social classes, as women with a long education and consequently better-paid jobs tend to postpone and limit child-breeding.In the last quarter of the last century, the incidence of breast cancer in Denmark showed an almost 2-fold difference from an standardised incidence ratio (SIR) of 0.77 in women in agriculture to an SIR of 1.39 for academics. The same pattern was seen for breast cancer mortality, with standardized mortality ratios (SMRs) of 0.75 and 1.29, respectively. 1 Childlessness in Denmark at a given age is furthermore known to be most common in women with a longer education, [3][4][5] and in the 1970s an increasing proportion of women completed longer education. 4,5 The present study was undertaken to assess the impact of reproductive behavior on the social class gradient in breast cancer occurrence in Denmark. Our objectives were to study whether the gradient across socioeconomic groups could be explained by the fertility differences, whether the gradient across educational groups could be explained by fertility differences and whether the effect of socioeconomic group on breast cancer incidence and mortality could be explained by education and vice v...

The relation between socioeconomic and demographic factors and tumour stage in women diagnosed with breast cancer in Denmark, 1983–1999

“…The social inequality at diagnosis observed in our study contrasts with the increasing risk for breast cancer with increasing education (Danø et al, 2003) and occupational group (Dano et al, 2004) in Denmark. It remains unclear whether the reason for the disparity by risk-group is delay in diagnosis or differing biology of cancers in the groups with less education and income compared with more advantaged groups.…”

Cancer risk by education in Iceland; a census-based cohort study

“…In a NorwegianSwedish study the educational gradient in breast cancer risk could be fully explained by established breast cancer risk factors [16]. On the other hand, in a Danish study, fertility patterns, did not explain the observed social gradient in breast cancer risk [17]. Among factors associated with an increased risk of breast cancer are low parity or nulliparity, high age at first birth, low age at menarche, high age at menopause and alcohol consumption, whereas breastfeeding and physical activity are associated with a decreased risk [18,19].…”

Birth outcome in women with breast cancer

“…Our data, however, did not show any important difference in male proportions between the offspring of breast cancer women and offspring of comparison mothers. It has been reported that women with high socioeconomic status have a higher incidence of breast cancer (Danø et al, 2004), while low socioeconomic status has been associated with adverse birth outcome (Luo et al, 2004). We were unable to adjust for socioeconomic status and therefore we may have underestimated the effect of the disease.…”