Gender effects in familial cancer

Very limited data are available on sex ratios in familial cancer. Such data would be valuable in the assessment of sex chromosome effects and of interactions between background and familial rates. We used the nationwide Swedish Family-Cancer Database on 10.2 million individuals and over 1 million neoplasms to analyze familial risks for male and female offspring by paternal and maternal concordant cancer. Sex ratios for familial cancer were derived for cancer at 15 sites shared by men and women. At 14 sites the sex ratio (male/female) for familial relative risk ranged between 0.78 and 1.41, with no evidence of sex preference, suggesting that sex chromosomes do not contribute to a noticeable extent to familial risks. Furthermore, in cancers where the background incidence varied extensively by sex, such as bladder cancer (sex ratio 2.82) and nonthyroid endocrine tumors (0.65), the familial effect was proportionate to the background incidence and the familial sex ratio was close to unity. In thyroid cancer, the familial sex ratio was 2.48 (1.54-3.98) and the background incidence ratio was 0.31. This was the first evidence of an inverse sex ratio in primary cancer, i.e., higher familial risk in the gender of low background risk. The high familial ratio, 2.85 (95% CI: 1.35-6.03), was due to thyroid adenocarcinoma, encompassing both papillary and follicular types.