Can reproductive pattern explain better survival of women with lung cancer?

We examined whether women's survival from lung cancer is influenced by hormonal factors associated with reproductive events. In all 4235 women and 4797 men born on 1 January 1935 or later with lung cancer diagnosed in 1978-1999 were identified in the Danish Cancer Registry and followed up to 31 December 2002 by linkage to the Central Population Registry. Cox regression analysis was used to estimate hazard rate ratios (HRs), and survival probabilities were calculated. Both nulliparous women and men without children had worse prognoses than those with children (women: HR 1.14; CI 1.03-1.26; men: HR 1.24; CI 1.15-1.34). The 5-year survival rate of nulliparous women with adenocarcinoma was 20.3%, while that for parous women was 20.5%; the corresponding rates for men were 13.0% and 16.6%. The number of children affected the risk for death in both sexes, indicating that the finding is not due to hormonal factors but to unmeasured elements such as socio-economic status or lifestyle factors related to parenthood.