1. ¹The Danish Epidemiology Science Centre, University of Aarhus, Vennelyst Boulevard 6, 8000 Aarhus C, Denmark
2. ²Laboratory for Mother and Child Health, Istituto Ricerche Farmacologiche 'Mario Negri', Via Eritrea 62, 20157 Milan, Italy
3. ³Department of Biostatistics, University of Aarhus, Vennelyst Boulevard 6, 8000 Aarhus C, Denmark
4. ⁴Laboratory for Stem Cell Research, Aalborg University, Gustav Wieds Vej 10, 8000 Aarhus C, Denmark

Correspondence: Dr R Campi, Laboratory for Mother and Child Health, Istituto Ricerche Farmacologiche 'Mario Negri', Via Eritrea 62, 20157 Milan, Italy. E-mail: campi@marionegri.it

Received 15 September 2003; Revised 17 December 2003; Accepted 17 December 2003; Published online 24 February 2004.

Abstract

The more men by whom a woman has children, the more diverse will be the foetal antigens of paternal origin introduced into her bloodstream, and we investigated whether this has an impact on subsequent cancer risks. By using population registries we identified 64 704 women who had children with at least two different partners from 1973 to 1996 in Denmark. We compared their cancer incidence with that of women who during the same time period had at least two births with no indication of partner change, adjusting for age, parity, socioeconomic factors and residence. The overall cancer incidence was more than 50% higher in women with two or more partners. Women having children with multiple partners had a higher incidence of cancer of the cervix and corpus uteri, a lower incidence of melanoma but a similar incidence of breast and ovarian cancer. Uncontrolled differences in lifestyle factors may explain the higher cancer risk associated with having multiple partners. The strong protective effect for melanoma was unexpected and deserves further study.