Skip to main content

Nordic Twin Study of Cancer


The Nordic Twin Study of Cancer (NorTwinCan), launched in 2008 and funded largely by the Ellison Foundation, is the largest twin study in the world available for the research of the heritability and familial risk of cancers such as prostate, breast, ovarian, and colon cancer.

This one-of-a-kind database is comprised of nationwide Nordic Twin Registries from Denmark, Sweden, Finland, and Norway and, remarkably, includes over 300,000 twins with data linked on cancer incidence and mortality over and average of five decades of follow-up.

Equally important is the comprehensive, multi-disciplinary team that disentangles the relative importance of environment versus genetic factors and related information relative to specific cancers. This group is comprised of prominent researchers and biostatisticians from the Harvard School of Public Health and National Twin Registries and academic institutions in the four Nordic countries that are involved.

In 2000, Paul Lichtenstein published “Environment and Heritable Factors in the Causation of Cancer – Analyses of Cohorts of Twins from Sweden, Denmark, and Finland,” in the New England Journal of Medicine, which has been cited in peer-reviewed literature more than 1200 times. Among other goals, this collaboration seeks to expand on that paper with an added registry (Norway) and a decade more of follow-up. This added data allows the researchers to analyze rare cancers, and when paired with the newly developed statistical methods, it gives more power and strength to the estimations of heritability.

Nordic twin studies have played a critical role in understanding cancer etiology and elucidating the nature of familial effects on site-specific cancers. The NorTwinCan consortium is a collaborative effort that capitalizes on unique research advantages made possible through the Nordic system of registries. It was constructed by linking the population-based twin registries of Denmark, Finland, Norway and Sweden to their country-specific national cancer and cause-of-death registries. These linkages enable the twins to be followed many decades for cancer incidence and mortality.
To date, two major linkages have been conducted: NorTwinCan I in 2011–2012 and NorTwinCan II in 2018. Overall, there are 315,413 eligible twins, 57,236 incident cancer cases and 58 years of follow-up, on average. In the initial phases of our work, NorTwinCan established the world’s most comprehensive twin database for studying cancer, developed novel analytical approaches tailored
to address specific research considerations within the context of the Nordic data and leveraged these models and data in research publications that provide the most accurate estimates of heritability and familial risk of cancers reported in the literature to date. Our findings indicate an excess familial risk for nearly all cancers and demonstrate that the incidence of cancer among twins mirrors the rate in the general population.
They also revealed that twin concordance for cancer most often manifests across, rather than within, cancer sites, and we are currently focusing on the analysis of these cross-cancer associations.

Selected publications

The Nordic Twin Study on Cancer - NorTwinCan
Harris J, Hjelmborg J, Adami HO, Czene K, Mucci L, Kaprio J.
Twin Res Hum Genet. 2019 Dec;22(6):817-823. Pubmed abstract


Cancer Incidence and Mortality in 260,000 Nordic Twins With 30,000 Prospective Cancers.

Skytthe A, Harris JR, Czene K, Mucci L, Adami HO, Christensen K, Hjelmborg J, Holm NV, Nilsen TS, Kaprio J, Pukkala E.

Twin Res Hum Genet. 2019 Apr;22(2):99-107. Pubmed abstract

Lung cancer, genetic predisposition and smoking: the Nordic Twin Study of Cancer.

Hjelmborg J, Korhonen T, Holst K, Skytthe A, Pukkala E, Kutschke J, Harris JR, Mucci LA, Christensen K, Czene K, Adami HO, Scheike T, Kaprio J; Nordic Twin Study of Cancer (NorTwinCan) collaboration.

Thorax. 2017 Nov;72(11):1021-1027. Pubmed abstract


Familial Risk and Heritability of Cancer Among Twins in Nordic Countries.
Mucci LA, Hjelmborg JB, Harris JR, Czene K, Havelick DJ, Scheike T, Graff RE, Holst K, Möller S, Unger RH, McIntosh C, Nuttall E, Brandt I, Penney KL, Hartman M, Kraft P, Parmigiani G, Christensen K, Koskenvuo M, Holm NV, Heikkilä K, Pukkala E, Skytthe A, Adami HO, Kaprio J; Nordic Twin Study of Cancer (NorTwinCan) Collaboration.
JAMA. 2016 Jan 5;315(1):68-76. Pubmed abstract

The Heritability of Breast Cancer among Women in the Nordic Twin Study of Cancer.

Möller S, Mucci LA, Harris JR, Scheike T, Holst K, Halekoh U, Adami HO, Czene K, Christensen K, Holm NV, Pukkala E, Skytthe A, Kaprio J, Hjelmborg JB.

Cancer Epidemiol Biomarkers Prev. 2016 Jan;25(1):145-50. Pubmed abstract

Cancer risk in opposite-sex and same-sex twins
Ahrenfeldt LJ.
ATLAS of Science. 2015 Nov. Online version

Risk of Sex-Specific Cancers in Opposite-Sex and Same-Sex Twins in Denmark and Sweden.
Ahrenfeldt LJ, Skytthe A, Möller S, Czene K, Adami HO, Mucci LA, Kaprio J, Petersen I, Christensen K, Lindahl-Jacobsen R.
Cancer Epidemiol Biomarkers Prev. 2015 Oct;24(10):1622-8. Pubmed abstract 

The heritability of prostate cancer-response
Hjelmborg JB.
Cancer Epidemiology, Biomarkers & Prevention. 2015 maj; 24(5):879. Online version

The Heritability of Prostate Cancer in the Nordic Twin Study of Cancer
Hjelmborg JB, Scheike T, Holst K, Skytthe A, Penney KL, Graff RE, Pukkala E, Christensen K, Adami HO, Holm NV, Nuttall E, Hansen S, Hartman M, Czene K, Harris JR, Kaprio J, Mucci LA.
Cancer Epidemiology, Biomarkers & Prevention. 2014 nov; 23(11):2303-10. Pubmed abstract

Media appearance

Nordic twins help reveal higher cancer risks
A comprehensive study of twins in Denmark, Norway, Sweden and Finland has led to new revelations about increased cancer risks among siblings.
The Local. January 6, 2016. Read online...


Nordic Twin Study of Cancer


EBB - Epidemiology, Biostatistics and Biodemography Department of Public Health University of Southern Denmark

  • Campusvej 55
  • Odense M - DK-5230
  • Phone: +45 6550 3029

Last Updated 20.10.2023