Wilms tumor remains the most common type of renal tumor in children, according to a large, international study. Meanwhile, the proportion of renal carcinomas among kids increased with age, and so did their incidence over time — which the authors think may have something to do with environmental factors.

In their study, researchers looked at more than 16,000 cases of malignant renal tumors collected across data from more than 308 population-based cancer registries on 5 continents. The total included 15,320 renal tumors in children aged 0 to 14 years and 800 renal tumors in teens aged 15 to 19 years. The study looked into the incidence of renal tumors in 15 world regions and across 5 ethnic groups in the US. The researchers also investigated time trends in incidence from 1996 to 2010 and trends during 4 decades (between the 1970s and the 2000s).

The age-standardized incidence rate (ASR) of renal tumors among children aged 0 to 14 years was 8.3 per million (95% CI, 8.1-8.4) and 1.4 per million (95% CI, 1.3-1.5) among adolescents aged 15 to 19. The highest ASRs in children were identified in North America and Europe, ranging between 9.1 (95% CI, 8.4-9.7) and 9.8 per million (95% CI, 9.4-10.2). In the US, the highest ASR was found for Black individuals, at 10.9 per million (95% CI, 10.2-11.6).

Wilms tumor was found to be the most common type of renal tumor in children aged 0 to 14 years, both in all the different world regions and in ethnic groups in the US. Wilms tumors also constituted more than 90% of all renal tumors in each age group from 1 to 7 years, but the proportion of renal carcinomas also rose with age.

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Among children aged 0 to 14, the researchers also identified 431 cases of kidney sarcomas (age‐standardized incidence rate [ASR], 0.2 per million, 95% CI, 0.2-0.3), and 327 cases of rhabdoid renal tumor (ASR, 0.2 per million, 95% CI, 0.2-0.2), which constituted 3% and 2% of all renal tumors.

For both major age groups examined in the study — children and adolescents — the incidence of renal carcinomas was highest in the Black population in the US. Moreover, the vast majority of 39 medullary carcinoma cases in the US, at 85%, were identified in the Black population.