Claire Vajdic

University of New South Wales

PLCO (Learn more about this study)

2010-0232

Sep 27, 2010

Sibship size and site- and morphology-specific adult cancer risk

There is mixed evidence of an association between sibship size and cancer risk. Sibship size is an indirect measure of exposure to infectious diseases in early childhood and possibly also exposures in utero. Compared to only children or children born into smaller sibship families, children born into larger sibship families have an increased likelihood of exposure to infectious agents and a younger age at first infection. Later born children are also exposed to higher levels of estradiol levels in utero. While there is consistent evidence of a positive association between sibship size and adult stomach cancer risk, the evidence is both inconsistent and limited for a number of other cancers diagnosed in adults, including solid and haematopoietic neoplasms. This inconsistency may be related to recent evidence of selection bias by socioeconomic status and thus family size in some case-control studies. We propose to conduct a pooled analysis across two cohort studies (PLCO and the NIH-AARP Diet and Health Study) to better understand the relationship between sibship size and adult cancer risk. By examining all cancers with at least 500 accrued cases, we will be able to assess the pattern of risk for cancers with and without an established infectious etiology, and those with and without a causal association with estrogen. We will also investigate the association between sibship size and specific morphological subtypes.