Academic journal article Environmental Health Perspectives

Male Breast Cancer Incidence and Mortality Risk in the Japanese Atomic Bomb Survivors-Differences in Excess Relative and Absolute Risk from Female Breast Cancer

Academic journal article Environmental Health Perspectives

Male Breast Cancer Incidence and Mortality Risk in the Japanese Atomic Bomb Survivors-Differences in Excess Relative and Absolute Risk from Female Breast Cancer

Article excerpt

Introduction

Female breast cancer is the most commonly occurring cancer among women in developed and developing regions of the world (WHO 2015). Male breast cancer is much rarer--the number of incident cases of male breast cancer is typically about 0.5-1% of the number of female breast cancers in many developed western populations (Landis et al. 1999; ONS 2012). There is a similar ratio of male breast cancer deaths to female breast cancer deaths (ONS 2004). Male and female breast cancer share some etiological features, although not all (Weiss et al. 2005).

Female breast cancer has been associated with exposure to moderate and high doses (> 100 mGy) of ionizing radiation in the Japanese atomic bomb survivors Life Span Study (LSS) cohort and in women who received radiotherapy (UNSCEAR 2008). A pooled analysis of eight cohorts suggested that excess relative risks of female breast cancer are (dependent on cohort) modified by age at exposure or attained age (Preston et al. 2002). There is emerging evidence to suggest that male breast cancer may also be radiogenic, in the LSS incidence data set (Ron et al. 2005) and in a population-based U.S casecontrol study (Thomas et al. 1994). However, possibly due to the small number of cases, Ron et al. (2005) did not report analyses of exposure response trend. There has been no similar study of male breast cancer in the latest LSS mortality follow-up (Ozasa et al. 2012).

In the United Kingdom, the Industrial Injuries Advisory Council (IIAC 2015) is currently considering amending the list of cancers arising from occupational exposure to ionizing radiation for which state compensation may be claimed, if exposure is sufficient to double the relative risk of disease. Included within these considerations is whether or not to recommend male breast cancer should be added to the list that currently includes female breast cancer: This has provided the motivation for this further analysis. Male breast cancer is currently regarded as a disease for which compensation can be paid if the probability of causation is sufficiently high by the U.S. Department of Labor, and the same relative risk model is used for both sexes (U.S. Department of Labor 2016). However, the U.S. National Cancer Institute RadRAT probability of causation calculation software does not have a model for male breast cancer (Berrington de Gonzalez et al. 2012).

In this paper, we analyze male and female breast cancer incidence and mortality in the latest versions of the LSS incidence (Preston et al. 2007) and mortality data (Ozasa et al. 2012). We assess the statistical comparability of measures of generalized excess relative risk and excess absolute risk between males and females, specifically focusing on dose-response trends and their modification by attained age, and age at exposure. Such generalized excess relative and absolute risk models have previously been shown to provide a good description of breast cancer risk in the LSS and in other radiation-exposed groups (Little and Boice 1999; Preston et al. 2002). We shall emphasize estimates of excess relative risk because of their ready applicability to estimate probability of causation (IAEA 1996).

Methods

Study Population and Data Sources

The LSS breast cancer incidence data used is the publicly available version of the data set analyzed by Preston et al. (2007). Details of the study population and methods have been published previously (Preston et al. 2007). Their analysis assessed cancer incidence over the years 1958-1998 in the two cities (Hiroshima and Nagasaki, Japan), and this should be roughly comparable with follow-up in the earlier publication of Ron et al. (2005); however, total numbers of cases differ slightly [see Supplemental Material A Table A2, and Table 1 of Ron et al. (2005)], which we discuss later. Likewise, the breast cancer mortality data set is the publicly available version of the data set analyzed by Ozasa et al. …

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