Article 28: Skin Cancer in PwMS

RESEARCH REPORT Skin cancer in people with multiple sclerosis: a record linkage study M J Goldacre, V Seagroatt, D Yeates, E D Acheson

J Epidemiol Community Health 2004;58:142?144

Objective: The prevalence of multiple sclerosis (MS) varies with latitude: it increases with distance from the equator in both hemispheres. To seek evidence on whether solar radiation is a protective factor for MS, this study investigated whether skin cancer, as an indicator of solar radiation, is less common in people with MS than in others.

Design: Analysis of a database of linked hospital records and death certificates.

Setting: The Oxford Region of the National Health Service, England.

Subjects: A cohort comprising all people in the database with MS, and comparison cohorts of people with other diseases.

Results: Skin cancer was significantly less common in people with MS than in the main comparison cohort (rate ratio 0.49; 95% confidence interval 0.24 to 0.91). There was no general deficit of cancer in the MS cohort, and no deficit of skin cancer in cohorts of people with other autoimmune or neurological diseases.

Conclusion: The findings support the hypothesis that solar radiation may have a protective influence on the development of MS.

The aetiology of multiple sclerosis (MS) remains obscure, but its remarkable global distribution may provide a clue to part of its causation. Among Europeans who have settled in North America, South Africa, Australia, and New Zealand there is a close relation between the prevalence of the disease and distance from the equator.

In North America MS is more common in Canada and the northern states of the USA than in the southern states, while in the southern hemisphere there is a regular gradation in the prevalence of MS in the opposite direction? from south to north.

These findings led to the suggestion that ??the more sunshine there is in a climate the less MS there appears to be?? and the hypothesis that ??such an influence could conceivably act directly, a certain skin dose of sunshine per unit time protecting the individual in some way??.2 One of the sun associated factors that showed a strong inverse correlation with MS in North American studies was lack of winter sunshine. This suggests that a minimum exposure throughout the year may be necessary to confer protection. Recent work has suggested that, as a mechanism, solar radiation might be one of the factors that influence the development of MS through an effect on the immune system.

It is generally accepted that the direct effect of solar radiation on skin is an important cause of skin cancer in fair skinned people. Most squamous and basal cell carcinomas in fair skinned people occur on sun exposed skin and are related to affected individuals? cumulative dose of solar radiation. Solar keratoses commonly precede the development of squamous cell carcinoma. There is also strong evidence that solar radiation contributes to the aetiology of melanoma of the skin in some way, but the association with duration of exposure to sunlight is less linear than that for the epithelial skin cancers. The association with melanoma may be related, in part, to intermittent, recreational sun exposure.

If solar radiation protects against MS, people with MS might have a lower than average risk of skin cancer. We tested this hypothesis using data from the Oxford record linkage study (ORLS).

METHOD The ORLS includes brief statistical abstracts of records of all hospital admissions (including day cases) in National Health Service (NHS) hospitals, and all deaths regardless of where they occurred, in defined populations within the former Oxford NHS region, from 1 January 1963 to 31 March 1999.

The hospital data were collected routinely in the NHS as hospital discharge statistics. They exclude patients treated in the private sector. The data about deaths were obtained by the ORLS from death certificates. Data collection covered two health districts from 1963 (population 850 000), six districts from 1975 (population 1.9 million) and all the eight districts of the region from 1987 (population 2.5 million). The data for each person were linked together routinely as part of the Oxford region's health information systems.

The MS cohort was obtained by selecting records of people aged 15 years and over with an admission for MS. The admission date was that of the first recorded admission for MS. It is not necessarily the first ever admission, which could have occurred outside the area covered by the database or before the start of the database. A reference cohort was constructed by similarly selecting records of people aged 15 years and over who had been admitted for various medical and surgical conditions. This was drawn from a standard ??reference?? group of patients that has been used in other studies of inter-relations between diseases. We identified any subsequent inpatient or day case care for skin cancers, and for all cancers, in these cohorts. We considered that the cancer rates in the reference cohort would approximate to those in the general population of the region while permitting for migration from it (data on migration of people were not available).