Cohabitation, infection and breast cancer risk.

For 50 years, the effect of age at first birth (AFB) has been thought to explain the strong association between breast cancer risk and age at first marriage (AFM), which was first reported in 1926. The independent effects of AFM, AFB and number of sexual partners adjusted for parity and other risk factors were estimated in reanalysis of a large international case-control study conducted in 1979 to 1982 (2274 breast cancers, 18209 controls) by unconditional logistic regression. Respective AFB and AFM breast cancer odds ratios (ORs) for ≥31 years relative to ≤18 years were 3.01 (95% CI 2.44-3.71; P(trend) < .0001) and 3.24 (95% CI 2.62-4.01; P(trend) < .0001) in univariate analyses. Among married parous women, these ORs fell to 1.38 (95% CI 0.98-1.95; P(trend) < .03) for AFB and 1.70 (95% CI 1.17-2.46; P(trend) < .002) for AFM when fitted together in multivariate analysis including other risk factors. A similar adjusted OR for AFM ≥ 31 years relative to ≤18 years was seen among married nulliparous women (OR 1.71, 95% CI 0.98-2.98; P(trend) < .001). AFM (a surrogate for age at starting prolonged cohabitation) is thus strongly associated with breast cancer risk. This suggests an effect of close contact. Identifying the (probably infective) mechanism might lead to effective prevention of breast cancer. The independent effect of AFB is smaller and could be due to residual confounding.

A case-control study of occupational contact levels in the childhood leukaemia cluster at Seascale, Cumbria, UK.

OBJECTIVES: To investigate adult occupational contact levels and risk of childhood leukaemia and non-Hodgkin's lymphoma (LNHL) in Seascale, an association found in other situations of rural population mixing (PM). DESIGN: Matched case-control study. SETTING: Seascale, Cumbria, UK. PARTICIPANTS: For each case of LNHL recorded in patients under age 25 years during 1950-2006, up to 20 matched controls were chosen and parental occupational details obtained; an exception was a single working young adult, whose own occupation (and that of controls) was used. PRIMARY OUTCOME MEASURES: Contact levels of occupations were categorised as: low/medium (reference group), high or very high contact levels, as in previous studies, with provision for certain unusual occupations. In particular, specialist policemen responsible for security and access at the nearby Sellafield nuclear complex were allocated to the highest contact category, and those Sellafield employees who worked in controlled areas to the middle (high) category. Since of possible bias, unusual contact aspects noted in the main research and development (R&D) building were reserved for a supplementary analysis. ORs were calculated for the occupational contact levels. RESULTS: Compared to the reference group, the social class adjusted ORs for the high and very high contact categories were 8.18 (95% CI 0.95 to 70.33) and 14.90 (1.20 to 184.90), respectively, with a significant trend across the categories (p value=0.024). In the supplementary analysis with R&D workers moved to the very high contact category, the OR for the latter became 29.68 (2.12 to 415.79), and the p value for trend, 0.011. CONCLUSIONS: The Seascale LNHL excess was most marked among those young people linked with high occupational contact levels; it is therefore not an exception to the pattern of family infection shown by other PM-related excesses. The findings have implications for the choice of controls in certain types of virus study.

Breast cancer and ages at first marriage and first birth: a new hypothesis.

The aim of this study was to examine available data on breast cancer and age at first marriage from a new perspective: that is, marriage involves the closest contact and contact effects are relevant to the question of infection, a possibility long considered in this disorder. The large Seven Country Study, carried out in 1964-1968, investigated age at first marriage; its reports were examined carefully for details of possible relevance. Intriguing gaps were noted in the grounds for the conclusion by this study that late age at first birth explained an earlier reported association with late age at marriage, with risks presented by age at first marriage for nulliparous, but not for parous, married women. Only in one centre, Glamorgan Wales, and only for two age groups could risks by combined ages at first marriage and first birth be derived. When both events occurred at age 30 or older, the risk estimate was 7.0 (95% confidence interval: 5.2, 9.1) relative to when both events occurred younger than age 20, whereas the corresponding risk was 1.4 (95% confidence interval: 1.1, 1.8) when age at first birth was 30 or older but marriage was younger than age 30. The above findings are consistent with an effect of age at first marriage, and a basis in contacts or infection is considered plausible. However, other explanations may exist, and this report primarily aims to encourage examination of the subject in other datasets, particularly where intersexual contrasts in infective exposures have probably existed.

Ethnic composition, age and sex, together with location and standard of housing as determinants of HTLV-I infection in an urban Trinidadian community

The presence of antibody to human T-cell leukaemia virus (HTLV-I) has been assessed in 2,143 men and women who represent 83 percent of all adults aged 35 to 69 years resident in a defined urban community in Trinidad. Individuals of African descent had a higher sero-positivity rate (7.0 percent) than those originating from India (1.4 percent), Europe (0 percent) or of mixed descent (2.7 percent). Women were infected more frequently than men, and the prevalence of infection increased with age in both sexes. Sero-positivity rates were significantly increased in adults who lived in housing of poor quality (p less than 0.001) or close to water courses (p less than 0.025). These data and others raise the possibility that one route of HTLV-I transmission may be via insect vectors under particular domestic circumstances.(AU)