Sensitivity analysis showed a nonsignificant difference in multiplicity proportions. Thus, all years were included in the analysis. The final number of first diagnosed BCCs after excluding 32 cases diagnosed outside of the country was 7226. No cases diagnosed in individuals aged < 30 years were excluded after review. There were 3100 cases in men (42·9%) and 4126 (57·1%) in women. For first BCC, the average age at diagnosis for the entire study period was 67·2 years for men and 65·2 years for women (P < 0·001). Overall, 71% of all BCCs in men and 72% in women (P = 0·21) were diagnosed in the Reykjavik region. Head and neck was the most common anatomical location for both men and women (62% and 55%, respectively) (P < 0·01). Next was the trunk (29% for men and women) (P = 0·56) and then the legs (3% for men, 8% for women) (P < 0·01).
Age-standardized Incidence Rates – by Sex
In 1981 the age-standardized incidence rates were 25·7 tumours per 100 000 for men and 22·2 per 100 000 for women (not statistically significantly different). The rates had increased approximately 2·33 times for men and 3·74 times for women by 2017 (Figure 1). After the period 1998–2002 the difference in incidence the between sexes became statistically significant, as can be seen in Figure 1 from the nonoverlapping 95% CIs. In the final 2013–2017 period, the WSR was 1·39-fold higher for women than for men (83·1 and 59·9 per 100 000, respectively). The largest increase in WSR was observed for women between 1995 and 2004, with a 1·49-fold difference (from 39·8 to 59·2). For men, the increase in WSR was more stable over time, with the WSR increasing 1·19-fold during the same period (35·5 to 42·4).
Histologically confirmed basal cell carcinoma in Iceland, age-standardized (world) incidence (5-year moving averages) from 1981 to 2017 for men (blue) and women (red), including 95% confidence intervals (dotted lines).
Age-standardized Incidence Rates – by Anatomical Location and Geographical Area
For all body sites, the WSR increased for both men and women from 1981 to 2017 (Figure 2). The higher total number of BCCs in women compared with men can be mostly accounted for by a rapid increase in truncal and leg lesions compared with head and neck lesions. In the 1981–1990 time period, 72% of BCCs were located on the head and neck in both men and women. In the 2009–2017 time period this percentage had decreased to 57% for men and 49% for women (P < 0·01), not because of a decrease in the number of cases, but because of a proportional increase in truncal and leg lesions in women.
Trends in age-standardized (world) incidence (5-year moving averages) of basal cell carcinoma according to sex, anatomical location and time period. (a) Men and (b) women.
There was a notable increase in BCC age-standardized rates for both Reykjavik and rural areas. Rates in rural areas were lower for both sexes (Figure 3). For 2009–2017, the difference in incidence between rural men (50·0 per 100 000, 95% CI 44·7–55·3) and Reykjavik men (62·2, 95% CI 58·2–66·2) was statistically significant. The difference between Reykjavik women (83·8, 95% CI 79·0–88·5) and rural women (72·4, 95% CI 65·7–79·2) was marginally significant.
Trends in age-standardized (world) incidence (5-year moving averages) of basal cell carcinoma according to time period, sex and residence (Reykjavik vs. rural areas). (a) Men and (b) women.
For the whole study period the annual percentage change in incidence was 2·99% for men and 4·12% for women. Figure 4 shows slopes for BCCs of the head and neck for the groups aged < 50 years and ≥ 50 years. No join points occurred. There was a marginally significant difference between the slopes in the < 50-year group: 0·11 (95% CI 0·05–0·17) for men and 0·24 (95% CI 0·17–0·31) for women. In the ≥ 50-year group there was no significant difference between the slopes: 2·89 (95% CI 2·38–3·40) for men and 3·26 (95% CI 2·66–3·86) for women.
Join-point analysis of basal cell carcinomas of the head and neck for men (blue) and women (orange), using age-standardized rates (world) per 100 000. (a) Age < 50 years and (b) age ≥ 50 years. ^ indicates that the slope is significantly different from zero at the alpha = 0·05 level.
For lesions of the trunk in the < 50-year group (Figure 5), join points occurred for women in 1993 and men in 1988. No join points were observed in the ≥ 50-year group. As with head and neck lesions, a more prominent difference between sexes was noted for the < 50-year age category compared with age ≥ 50 years. For leg lesions, statistically significant join points occurred for women aged < 50 years in 2004 (slope increased from 0·0 to 0·36) and for women aged ≥ 50 years in 1992 (slope increased from 0·00 to 1·34). For men there was no corresponding increase in leg lesions.
Join-point analysis of basal cell carcinomas of the trunk for men (blue/dark green) and women (orange/light green), using age-standardized rates (world) per 100 000. (a) Age < 50 years and (b) age ≥ 50 years. ^ indicates that the slope is significantly different from zero at the alpha = 0·05 level.
When accounting for multiplicity, the total number of BCCs during the entire study period was 12 432 lesions in 7226 individuals. Similar numbers of lesions on average were diagnosed in men and women (1·7 and 1·73, respectively). Overall, 92% of individuals, both men and women, had between one and three lesions. During the first period of the study (1981–1990) a slightly higher proportion of men had multiple lesions (35%) compared with women (33%; P = 0·74). During the last period (2009–2017) the multiplicity proportions had decreased to 25% for both sexes.
The median time interval between first and second BCCs was 2·2 years for women (range 0–34) and 2·1 years for men (range 0–30). The overall median interval between all BCCs that developed was 1·4 years (range 0–34) for women and 1·3 years (range 0–30) for men. This difference between sexes was not statistically significant. Table 1 demonstrates age-specific rates (ASRs) analysed by age group and sex. Overall, women had higher ASRs for both single and multiple tumours, with the exception being the ≥ 65-year single-BCC category, where men had a higher ASR.
Lifetime and Cumulative Risk
In the 2009–2017 time period the lifetime risk for women was 10·1%, compared with 7·3% in men (P < 0·01). This is an increase from the 1981–1990 period, when the lifetime risk was 3·2% for women and 2·8% for men (P = 0·1). The risk for women aged < 40 years saw the highest proportional increase: sixfold (from 0·1% to 0·6%), compared with threefold for men (from 0·1% to 0·3%).
The British Journal of Dermatology. 2020;183(5):847-856. © 2020 Blackwell Publishing