Mapping of cancer risk and cause-specific mortality among employees in the Norwegian offshore industry

In this study, we will also conduct causal studies of female offshore workers, who have been little studied before.

Background

Exploration of oil and gas on the Norwegian continental shelf started in the middle of the 1960s, and the first oil was produced in 1971. The activity expanded rapidly throughout the 1970s and -80s, and by the end of 2016, 80 petroleum fields were in production.

Offshore petroleum work takes place under hostile conditions, which challenge the safety and the protection of workers' health. Carcinogens in raw oil, in additives, and in emissions may lead to with increased risk of long-term chronic diseases such as cancer.

Earlier studies among Norwegian offshore workers have shown that women, who constitute 10 percent of the workers, are at increased risk of cancer of all types taken together, involving leukaemia, malignant melanoma, and lung cancer.

We plan to assess the risk of respiratory cancer (lung and pleura) , specifically among men, according to occupational exposures with adjustment for smoking habits and work outside the offshore sector. Cancer of the urinary bladder is in excess among male offshore workers, and the study will explore the relationship between urinary tract carcinogens and the risk of bladder cancer and kidney cancer.

Study aims

The primary objective of the project is to describe the risk of cancer among Norwegian offshore petroleum workers, and clarify whether cancer incidence in the group is linked to exposures that have occurred in the offshore working environment. 

Material and methods

The survey-based cohort was established by the CRN and designed for use in prospective studies of cancer in offshore workers. Invitations with questionnaires were distributed to the home adresses according to lists provided by production and contractor companies, schools, registries and archives, which all had a link to offshore activity. Individuals reporting offshore work constitute the 28 000 members of the CRN Offshore Cohort.

Cancer incidence data at the CRN will be linked with the data reported on the questionnaires. This includes detailed work history offshore with dates of start and stop for up to eight employment periods, as well as work outside the offshore industry, and some basic lifestyle factors (smoking, alcohol consumption, anthropometry, and diet). Information relevant for exposure assessment is derived from the questionnaires, such as occupational group, type of employer, calendar period of employment, and duration of employment.

Analyses that compare cancer incidence in the study group with that of the Norwegian population will be performed for the full cohort and subgroups. Expected numbers of cases are based on person-years by age, sex and period of observation multiplied with corresponding background rates for the general population.

Project status

In December 2017, the Cancer Registry of Norway received a grant of 13.40 million NOK from the Research Council of Norway. Two PhD candidates started working on the project in 2019, with one defending his thesis in 2022 and the other defending her thesis in 2024. In addition, two postdoctoral fellows have been employed on the project.

We are currently concluding the project and preparing the final results for publication.

Our research on Norwegian offshore petroleum workers has revealed several key findings:

• We published a cohort profile paper showing an excess of cancers of all types combined in both male and female offshore workers. Specifically, risks of cancers of the pleura, melanoma skin, breast, prostate, and leukemia were heightened compared to general population. Cohort Profile: Norwegian Offshore Petroleum Workers (NOPW) Cohort.
• We found that exposure to ultraviolet radiation (UVR) is linked to an increased risk of skin cancers, such as melanoma and squamous cell carcinoma (SCC), in both male and female offshore petroleum workers. We suggest that Northern hemisphere offshore petroleum workers may benefit from targeted sun protection advice to reduce skin cancer risk. Ultraviolet radiation and risk of cutaneous melanoma and squamous cell carcinoma in males and females in the Norwegian Offshore Petroleum Workers cohort.
• We noticed that female offshore workers with more than six years of night shift had higher breast cancer risk compared to those who only worked daytime, but the result was not significant. More research with larger groups is needed to explore these connections further. Night shift work, chemical coexposures and risk of female breast cancer in the Norwegian Offshore Petroleum Workers (NOPW) cohort: a prospectively recruited case-cohort study.
• We discovered that working rollover shifts is associated with a higher risk of prostate cancer compared to day work, especially with long-term exposure. However, we found no link between exposure to chlorinated degreasing agents and the risk of aggressive prostate cancer. Night shift work and risk of aggressive prostate cancer in the Norwegian Offshore Petroleum Workers (NOPW) cohort.
• We suggest that high cumulative and long-term exposure to benzene may be associated with an increased risk of bladder cancer. Experts in industrial hygiene developed industry-specific benzene job exposure matrices, but we could not determine if the risk is due to benzene alone or other related chemicals. Further studies are needed to evaluate the impact of benzene and similar substances on bladder cancer risk in petroleum workers. Exposure to benzene and other hydrocarbons and risk of bladder cancer among male offshore petroleum workers.
• We found that asbestos exposure in the NOPW cohort was associated with an increased risk of pleural mesothelioma. Our results also show that asbestos exposure occurring before offshore employment was associated with pleural mesothelioma risk. Exposure to fibres and risk of pleural mesothelioma in the Norwegian Offshore Petroleum Workers cohort.

Allumni

• Fei Chih (Phillip) Liu, PhD student 2019–2022, Disputation 23 Sept 2022
• Nita Kaupang Shala, PhD student 2019-2024, Disputation 2 Sept 2024
• Leon Alexander Mclaren Berge, Postdoctoral fellow

REC: The project is approved by the Ethical Committees, project no: 136984 

Funding: The project is funded by the Research Council of Norways programme PETROMAKS2.