An international study has identified a fourfold increase in cutaneous squamous cell carcinoma risk among younger generations of Tasmanian women, highlighting a growing burden of skin cancer linked to cumulative UV exposure.
Women are experiencing a faster generational rise in cutaneous squamous cell carcinoma (cSCC) than men across several countries, with Australian researchers identifying a particularly pronounced increase in Tasmania.
The QIMR Berghofer-led study, published in the British Journal of Dermatology, found that Tasmanian women born in 1984 had four times the cSCC risk of women born in 1959, after adjusting for age and period effects (rate ratio 4.01, 95% CI 2.33–6.89).
However, the researchers cautioned that estimates for younger birth cohorts were based on relatively few cases and shorter follow-up and should not be interpreted as lifetime cancer risk.
The findings emerged from an analysis of cancer registry data spanning 1989 to 2020 across seven populations in Australia and Europe, with researchers identifying substantially greater increases in cohort-specific cSCC risk among women than men in five of the seven populations.
Lead researcher Dr Catherine Olsen said the findings revealed a striking difference between cSCC and melanoma.
“We were quite surprised to see that SCC incidence was rising faster in women across generations compared to men. That’s a different pattern to what we see with melanoma,” Dr Olsen said.
The study used age-period-cohort modelling to examine cSCC and invasive melanoma incidence in Tasmania, Norway, Sweden, Finland, Denmark, Scotland, and the Netherlands.
The researchers calculated birth cohort rate ratios relative to people born in 1959, adjusting for the effects of age and calendar period, to investigate whether generational changes in cancer risk differed between men and women.
The strongest female-predominant cohort effects were observed in Tasmania, Norway, Denmark, Sweden, and the Netherlands. Finland and Scotland showed comparatively little divergence between the sexes.
Importantly, the differences were evident among people born before 1959, suggesting that the trend reflected long-standing changes in exposure rather than more recent behavioural shifts.
In contrast, melanoma cohort effects were broadly similar between men and women across most populations, with some countries showing larger increases among men.
The researchers said the difference was consistent with the distinct relationships between the two cancers and ultraviolet radiation.
While melanoma has a more complex association with intermittent, high-intensity UV exposure and childhood sun exposure, cSCC risk is strongly and dose-dependently associated with cumulative lifetime UV exposure.
The researchers said the findings suggested that generational changes in sun exposure, particularly among women, may be contributing to the increasing cSCC burden.
“There are changes that have happened over successive generations in terms of recreational exposure, also occupational exposure, and we are seeing an increased burden in women,” Dr Olsen said.
“It’s important that the community understands that because it is a preventable cancer.”
The researchers noted that the female-predominant increase was evident in generations born well before commercial tanning beds became widely available.
They suggested that changing cultural attitudes towards tanning, outdoor recreation, and clothing may have contributed to greater cumulative UV exposure among women over successive generations.
However, men continue to have higher absolute cSCC incidence rates than women, despite the faster relative increases observed among women in most populations.
Tasmania stood out as having a particularly pronounced female birth cohort effect, which the researchers suggested could reflect the interaction between high ambient UV radiation and changing recreational sun exposure.
The findings may also have implications for other high-UV environments, including mainland Australia and New Zealand.
The analysis revealed substantial geographical differences in the age at which cSCC incidence overtook melanoma incidence.
In Tasmania, cSCC incidence exceeded melanoma incidence from approximately 42 years of age, compared with around 72 years in Finland and Norway.
The median age at cSCC diagnosis was consistently older than for melanoma, although the gap was considerably narrower in Tasmania than in the European populations. Across the six European populations, the difference in median age at diagnosis ranged from 12 to 15 years among men and 18 to 22 years among women. In Tasmania, the corresponding differences were six and 15 years.
Senior author Professor David Whiteman said the findings highlighted the need for greater recognition of the increasing cSCC burden.
“This really is almost like a flag going up saying this is a problem that’s not going away. It’s becoming more common, and squamous cell cancers are eminently preventable,” Professor Whiteman said.
“We believe that almost all of them are caused by exposure to the ultraviolet rays in the sun.”
The researchers also examined whether changes in cancer registration practices could account for the observed trends.
Although improvements in registration and diagnostic reporting may have contributed to increasing recorded incidence, they considered these unlikely to explain the consistent sex-specific differences across populations.
They acknowledged that the ecological study design could not establish causation at an individual level and that differences in registry completeness, coding, and healthcare-seeking behaviour could affect comparisons.
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The findings also highlighted limitations in Australia’s national skin cancer surveillance.
Tasmania remains the only Australian jurisdiction to routinely register both cSCC and basal cell carcinoma, despite keratinocyte cancers accounting for a substantial burden of skin cancer treatment.
The researchers warned that incomplete cancer registration could obscure the true scale of the problem and limit efforts to plan prevention and healthcare services.
They also noted that while melanoma incidence was stabilising in several high-risk countries, cSCC incidence continued to rise, potentially placing increasing demands on dermatology and other healthcare services.
The researchers called for greater attention to cSCC in skin cancer prevention, screening, and early detection discussions, arguing that the growing disease burden remained under-recognised.
“As melanoma incidence stabilises in many high-income countries, cSCC is emerging as the dominant and growing skin cancer burden, yet this shift has not been widely recognised in clinical practice or by the research community and is not yet reflected in the priority given to cSCC in discussions regarding skin cancer screening or early detection initiatives,” they concluded.
“In many high-risk populations, cSCC is not even captured in cancer registration systems, obscuring the true scale of the problem.
“A meaningful component of the increase in cSCC incidence appears attributable to generational increases in UV radiation exposure in both sexes, with a particularly pronounced effect in women.
“Primary prevention efforts targeting cumulative sun exposure across the full life course, and particularly in high ambient UV radiation settings, may offer significant opportunities to reduce future cSCC incidence.”
