Basal Cell Carcinoma: An Emerging Epidemic in Women in Iceland

J.A. Adalsteinsson; D. Ratner; E. Olafsdóttir; J. Grant-Kels; J. Ungar; J.I. Silverberg; A.K. Kristjansson; J.G. Jonasson; L. Tryggvadottir

Disclosures

The British Journal of Dermatology. 2020;183(5):847-856. 

In This Article

Discussion

Although skin cancer used to be rare in Iceland, BCC has now become one of the cancers with the highest incidence in the Icelandic population, surpassing lung and colon cancer, but not prostate and breast cancer.[15] The country's capital, Reykjavik, has the lowest UVI of all world capitals and has on average a higher proportion of cloudy days than sunny days.[16] The WSR in Iceland is among the lowest reported (60 for men, 83 for women, per 100 000), with lower rates reported in Malta, Slovenia, Croatia and Lithuania,[6,17,18] despite Iceland's UV exposure being dramatically lower than in these countries. Thus, there does not seem to be a clear correlation between latitude and BCC incidence in Europe.[6] While the head and neck region was the most commonly affected location in this study, the incidence of leg and truncal lesions is increasing at a much faster rate. It is thus unlikely that natural background UV in Iceland is playing a significant role in this increase, as these anatomical locations are usually concealed outdoors in this population.

We noted a significantly higher BCC incidence in women than in men, as well as a greater increase in incidence, with women also being younger when diagnosed with their first BCC. A statistically significant higher incidence in women has not been observed previously, to our knowledge, in a whole-population epidemiological study.[18–25] In some areas that tend to have high overall background UV exposure, men have an incidence rate that is almost twice that of women.[26–30]

There are a few potential explanations for this observed sex difference. A 2002 survey conducted in the Reykjavik area indicated that 70% of women and 35% of men had used a tanning bed. This difference was especially pronounced in Icelandic teenagers: 50% of teenage girls had used a tanning bed in the previous year, compared with 30% of boys. It has been hypothesized that tanning bed exposure at a young age might exponentially increase BCC risk at a later age.[9,14,31] Women might also be more diligent with skin cancer screening, leading to discovery of BCCs on the legs and trunk that might otherwise have gone unnoticed. Some parts of the southern USA have considerably less access to dermatology care than Iceland, yet their BCC rates are much higher in comparison. This suggests that while increased screening might play some part in the increased incidence that has been observed, it cannot explain the whole picture.[28,30]

BCC rates in rural areas in Iceland were lower overall than in Reykjavik. This is the opposite of what is presumed to be the case in the USA and Australia, with individuals in rural areas thought to be at increased risk of developing BCCs due to occupational sun exposure.[32] The high rates observed there in rural areas in men are most likely due to chronic background occupational UV exposure.[33] In Iceland, the greater number of cloudy days and low UVI create a sun-protective environment for outdoor workers. Tanning bed use is comparable between Reykjavik and rural areas, but rural Icelanders might be less likely to see a dermatologist regularly due to low access.[14,31] Men also tend to be less diligent in their day-to-day sunscreen use.[34] Preventive efforts in Iceland and other countries with low background UVI might thus be more effective than in other countries with a high UVI and light-skinned populations. Theoretically it is easier for individuals to avoid high-risk behaviours such as tanning bed use, or to apply sunscreens in the little time spent in high UVI zones, rather than to avoid daily chronic UV exposure.

Tanning booths are an avoidable source of exposure to highly carcinogenic UV radiation, which increases the risk of both melanoma and nonmelanoma skin cancers.[35] The fact that there does not generally seem to be a relationship between latitude and BCC incidence in Europe could partly be explained by the increased use of tanning beds seen in Iceland between 1979 and 2004, as well as increased travel abroad. In 1979 there were only three sunbed salons in Reykjavik. By 1988 this number had increased to 56 facilities with 207 sunbeds.[10] The average of 2·8 tanning bed sessions per year in 2004–2007 in Iceland was around two to three times higher than in neighbouring countries, with a rapid decline in tanning bed use after the year 2004. In 2005, the number of publicly available sunbeds in the Reykjavik area had decreased to 144, and it further decreased to 97 in 2008.[10]

The significant join points noted in this study were on the trunk in men aged < 50 years in 1988 and in women aged < 50 years in 1992, and on the legs in 1992 for women aged ≥ 50 years and in 2004 for women aged < 50 years. These are anatomical locations not normally exposed to the sun in Iceland. All of these join points occurred within the height of tanning bed usage in Iceland (1979–2004). Interestingly, the join points occurred mostly in individuals aged < 50 years, but a 2001–2002 survey showed that 16% of women and 12% of men aged 20–39 years had used a solarium more than 100 times during their lifetime. In contrast, these proportions were 2% and 1% among women and men aged ≥ 50 years.[10,14,31]

Another potential reason for the increase in BCC incidence is travel abroad. The frequency of travelling abroad for Icelanders has increased considerably, from 65 941 yearly voyages to 937 315 between 1970 and 2006. Young Icelanders make fewer cumulative trips abroad but have higher cumulative tanning bed use than older Icelanders.[14] In 1988 and 1993 a join point was noted for truncal lesions for men and women < 50 years of age, but no join point was seen in individuals aged ≥ 50 years, possibly suggesting that a behavioural change might have occurred in the < 50-year group, which had less impact in the ≥ 50-year group. We lack sex-specific travel data, which could help delineate further the differences observed between sexes in this study. The reason for the sex-specific increase in leg lesions in women is unclear, but it could be a combination of tanning bed exposure, increased travel abroad and increased screening.[14]

An increase in truncal lesions in women was also reported in a 2010 study looking at melanoma in Iceland, which demonstrated a rapid increase in truncal lesions in women after 1992, and was attributed at least in part to use of tanning beds.[14] In that study, a decrease was seen in melanoma incidence after 2001, which was attributed to population-wide educational efforts against the use of tanning beds.[14] However, we do not see the same trend for BCC incidence. This might be explained by UV exposure having a more immediate effect on melanoma risk, with risk rapidly falling off 2–3 years after exposure. This might not be true for BCCs, where risk of development after UV exposure may be more prolonged.[14] It is not clear what the lag time is between UV exposure and increased risk of BCC development, but it might be as low as 2 years.[36]

To our knowledge, this is the first whole-population study investigating BCC multiplicity. A recent study exploring multiplicity rate estimates throughout Europe reported that for total estimates of BCC incidence, the first BCC diagnosis should be multiplied by 1·3.[17] Our study indicated that the rate should be multiplied by 1·7, implying that BCCs might be an even larger healthcare burden worldwide than previously thought. The median interval between development of BCCs decreased between the third and fourth BCC diagnoses (1·3 and 1·4 years for men and women, respectively) compared with that of the first and second diagnoses (2·1 and 2·2 years, respectively), supporting that more frequent surveillance might be warranted for individuals who have developed more than two lesions. The reason for the decreased multiplicity seen with time throughout the study period is likely to be in part due to shortened follow-up for individuals diagnosed late in the study.

This study's main weaknesses are its retrospective nature and the resulting inability to analyse specific characteristics of individuals developing BCCs.

In conclusion, these data show a significant public health problem in a country with limited UV radiation. There is a notable increase in BCC lesions, especially in women, which correlates with both a period of increase in tanning bed popularity and increasing travelling abroad. The trends observed in this study imply that BCCs are an even larger problem worldwide than previously thought, with behavioural differences existing between sexes that should be taken into consideration when planning much needed educational initiatives to decrease the incidence of skin cancer.

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