Melanoma cases rise despite unchanging mortality rate

Key takeaways:

• From 1999 to 2019, the incidence of invasive melanoma cases increased by 2.5-fold.
• Mortality varied slightly over the years but did not yield a significant trend.

Researchers found an inexplicable rise of melanoma incidences despite an unchanging mortality rate, according to a study.

“From 1990 through 2019, the age-standardized incidence of cutaneous melanoma increased globally on average by 1.13% per year, while the age-standardized mortality declined by 0.27%,” Jesper Bo Nielsen, MSc, PhD, professor of risk analysis and risk communication in the research unit of general practice at University of Southern Denmark, and colleagues wrote. “This discrepancy is not well explained.”

To explore the potential reasons behind this trend, as well as analyze the rise of cases, researchers conducted a register study.

The researchers found that a total of 1,434,798 biopsies were taken from 704,682 individuals from 1999 to 2019. The mean age at biopsy was 39.8 years in men and 37.4 years in women, with women comprising 65% of biopsied patients.

From 1999 to 2019, the incidence of invasive melanoma cases increased by 2.5-fold. The rate of biopsies performed from 1999 to 2011 increased by 153% in men and 118% in women. However, after 2011, biopsy rates fell by 20% in men and 22% in women.

From 1999 to 2019, the incidence of melanoma in-situ cases increased astronomically with cases rising 476% in men and 357% in women. Even more so, the incidence rates of atypical melanocytic lesions increased by 1,928% and 1,686% in men and women, respectively.

On the other hand, melanoma mortality varied slightly over the years, but the researchers did not detect any significant trend.

According to the authors, possible factors that may be causing melanoma incidences to increase include ultraviolet exposure; improved melanoma treatment; a higher rate of diagnostic activity in both the absence and presence of overdiagnosis; a drop in pathologists’ diagnostic threshold; and a rise in clinicians’ propensity to remove suspected lesions.

The authors claim that there is no evidence to suggest an increase in UV exposure in Denmark in the last 30 years, making this factor unlikely.

The researcher noted that the incidence rates were strongly correlated with biopsy rates. Even more interesting is that these biopsy rates occurred most among young patients, aged 15 to 44 years, especially women — an observation that the researchers labeled as “paradoxical” seeing as this age range experiences the lowest rates of melanoma.

The researchers hypothesize that lowered threshold of melanoma diagnosis among pathologists, increased diagnostic activity in the presence of overdiagnosis and introduction of immunotherapy for melanoma could explain the discrepancy between incidence and mortality. However, this cannot be confirmed.

“Our data do not prove that any one of the explanatory factors is the reason for increasing incidence of nevi and melanoma in the presence of constant mortality,” they concluded.