Baku, January 9, AZERTAC

Twins carry a significant excess familial risk for cancer overall and for specific types of cancer, including prostate, melanoma, breast, ovary, and uterus, according to a study published in JAMA.

An international team of researchers sought to estimate the familial risk and heritability of cancer types in a large twin cohort. The prospective study included 80,309 monozygotic and 123,382 same-sex dizygotic twin individuals (N=203,691) within the population-based registers of Denmark, Norway, Sweden, and Finland. The researchers followed the twins for a median of 32 years between 1943 and 2010. Within the study group, 50 990 individual persons died of any cause, and 3804 emigrated and were lost to follow-up.

The researchers used time-to-event analyses to estimate risk of cancer in a person given a twin's diagnosis of cancer (familial risk) and the proportion of variance in cancer risk due to interindividual genetic differences (heritability). Follow-up was via cancer registries.

Study findings showed 27 156 incident cancers diagnosed in 23 980 individuals; this translates to a 32% cumulative incidence of cancer. Cancer diagnoses were made in both twins in 1383 monozygotic pairs and 1933 dizygotic pairs, with diagnoses of the same cancer type in 38% of monozygotic and 26% of dizygotic pairs.

Excess cancer risk was seen in twins whose co-twin had a cancer diagnosis, with estimated cumulative risks being an absolute 5% higher in dizygotic twins and an absolute 14% higher in monozygotic twins whose twin also developed cancer compared with the cumulative risk in the overall cohort (32%).

The researchers report monozygotic twins have higher cumulative risks and significant familial risk compared with dizygotic twins. Overall heritability was 33%. Significant heritability was seen for skin melanoma, prostate, nonmelanoma skin, ovarian, kidney, breast, and corpus uteri cancers.