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).

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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.

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.

When the researchers looked at time trends in incidence during 1996 to 2010, they found that the incidence rates of renal tumors in children ages 0 to 14 years were stable because the incidence of Wilms tumor remained stable as well. However, they did find an increase in the incidence of rhabdoid renal tumor and renal carcinomas in the same age group — with the latter being mostly due to the significant increase of the condition in females (Average annual percent change [AAPC], 4.2, 95%CI=0.9, 7.6).

There was also an increase in incidence of renal carcinomas in males ages 15 to 19 (AAPC=3.7, 95%CI=0.3, 7.1), which contributed to the increased for the entire age group (AAPC=3.2, 95%CI=0.5, 5.9) even though no increase was observed in females of that age.

The overall rise in renal carcinoma incidence was also present when the investigators looked at four decades of data between the 1970s and the 2000s. These data displayed a doubling of renal carcinoma incidence from 0.1 to 0.2 per million (IRR=2.0, 95%CI=1.5, 2.7). In contrast, the incidence of Wilms tumor increased only slightly from 6.9 to 7.7 per million (IRR=1.1, 95%CI=1.0, 1.2) during this same period.

One of the most concerning findings in the report was the increase in the incidence of renal carcinomas, James B. Fahner, MD, FAAP, division chief, pediatric hematology oncology, BMT, palliative care at Helen DeVos Children’s Hospital at Spectrum Health in Grand Rapids, Michigan, who was not involved in the study, said in an email. “Unlike the primitive Wilms tumor, with predominantly genetically influenced origins, renal carcinomas may have significant, yet largely undetermined, environmental links,” he said. “How diet, medications, toxins, obesity, and other social determinants of health might be among the sources for this increased incidence could be the most powerful take away message of this work; a cautionary tale worthy of close continued scrutiny.”

In adults, environmental risk factors such as smoking, obesity, and workplace exposures are known to raise the risk of renal carcinomas — but in children the impact of environmental factors is less clear, Carolyn Fein Levy, MD, head of the pediatric oncology, rare tumor, and sarcoma (PORTS) Program at Cohen Children’s Medical Center, New Hyde Park, New York, who was not involved in the study, said in a phone interview. She noted that there could potentially be a link between the increased incidence of obesity and the increased incidence of renal carcinomas in adolescents, but more research would need to be conducted to determine whether that’s really the case.


Nakata K, Colombet M, Stiller, CA, Pritchard‐Jones, K, Steliarova‐Foucher, E. Incidence of childhood renal tumours: an international population‐based study [published June 16, 2020]. Int J Cancer. doi: 10.1002/ijc.33147

This article originally appeared on Cancer Therapy Advisor