The Semipalatinsk nuclear test site (SNTS) covers 18 500 km2 near the city of Semey, previously known as Semipalatinsk, in eastern Kazakhstan, where, in 1949-1989, the Soviet Union conducted 456 nuclear tests. In 1949-1962, 118 nuclear tests were conducted above ground and in the atmosphere, emitting radioactive contamination (release) into the atmosphere. Some of these releases caused radioactive plumes that exposed people and territories adjacent to the site, in particular the former Semipalatinsk oblast.

In the past two decades, various groups of researchers have initiated two cohort studies to assess the health effects of exposure to fallout from Soviet nuclear weapons testing among residents living near the SNTS. The first cohort, referred to as the historical cohort, consists of 10 exposed settlements and 6 control, or unexposed, settlements. This cohort contains 9 850 exposed and 9 604 unexposed residents born before 1 June 1961. The second cohort, assembled more recently and referred to as the new cohort, comprises inhabitants from 14 exposed villages and 6 control, or unexposed, villages. The new cohort includes 18 204 people who received varying doses of whole-body radiation.

Overall, the health effects of exposures to fallout from the SNTS among the residents living nearby have not been well investigated. The SEMI-NUC project, which was a support action, brought together scientists from Europe, Kazakhstan, and Japan to assess the feasibility of uniting these two cohorts and establishing a long-term, prospective follow-up study of the health effects from chronic exposure to low doses of radiation.

After reviewing sources of information and data availability on cancer incidence, it was concluded that a future cohort study of cancer incidence and cardio-vascular diseases in relation to early life exposure is feasible. A pilot study should first be conducted to test the quality of information on risk factors and examination results of exposed individuals.

A follow-up of the natural history of the thyroid nodules that were ultrasound-detected during screening examinations performed by NCI and Kazakh scientists in 1998 was also judged to be important and feasible. It is possible to carry out studies both on cancer and non-cancer mortality risks in a cohort of people exposed around the SNTS, because of the systematic follow-up of the population in the NIIRME registry and regular collection of information on death cases and causes by NIIRME researchers.