Steep rise in skin cancer since 1960s

The risk of developing more than one skin melanoma over a ten-year period has seen a ten-fold increase in Sweden since the 1960s, a new study by researchers at Karolinska Institutet and Lund University published in the Journal of the National Cancer Institute reports. The researchers suspect that the increase is due to a change in holiday customs with more active sunbathing and overseas trips to southern climes.

"There are many health benefits to being outside, but it would be good if studies like this could encourage people to protect their skin better and find other ways to enjoy their holidays than by sunbathing," says principal investigator Hildur Helgadottir, consultant at Karolinska University Hospital in Solna and researcher at the Department of Oncology-Pathology, Karolinska Institutet.

Skin cancer of the melanoma type is one of the fastest increasing tumor diseases in numerous countries, including in Sweden, where there were 4,543 new cases of invasive melanoma and 508 melanoma-related deaths reported in 2018. The main cause of this constant increase is thought to be an excessive exposure to UV radiation.

High degree of coverage and reliability

Using the Swedish Cancer Register, researchers have now studied trends in the risk of developing more than one skin melanoma. The strength of the register lies in its long history and its high degree of coverage and reliability.

"The Cancer Registry started in 1958, which is roughly when Swedes started to go on package holidays to the sun," says Dr. Helgadottir. "More active sunbathing and overseas trips to southern climes have led to more UV exposure of the Swedes' often sun-sensitive skin. This is probably one important reason for the sharp rise in the risk of developing recurrent melanoma."

The researchers studied individuals who had developed their first skin melanoma in the 1960s, 1970s, 1980s, 1990s and 2000s and how common it was for them to develop additional melanomas over a ten-year period. In the 1960s, only 0.7 percent of the cohort developed more than one melanoma, but since then the risk has gradually increased to about 7 percent in the 2000s. Moreover, a significant proportion of the 2000s cohort developed more than two melanomas, and this was previously very rare. The increase was more dramatic amongst men and older individuals.

The population as a whole

Another question was whether the increase in risk for multiple melanoma was only a reflection of the observed increase in melanoma for the population as a whole. However, the results showed that the upgoing curve for multiple melanoma was much steeper than that for the general increase in risk.

"This trend is serious, since earlier research has shown that people who develop more than one melanoma have a worse prognosis," says Dr. Helgadottir. "Even though awareness of the risks of UV radiation has increased, reports from the Swedish Radiation Safety Authority show that Swedes continue to devote much of their holidays to active sunbathing, and half report that they have been sunburnt. This is the first study to demonstrate how the risk of developing multiple melanoma has increased over time. I think it is very likely that a similar trend would be found in other countries that have seen an upward melanoma curve."