Incidence patterns of childhood non-Wilms renal tumors: Comparing data of the Nationwide Registry of Childhood Hematological Malignancies and Solid Tumors (NARECHEM-ST), Greece, and the Surveillance, Epidemiology, and End Results Program (SEER), USA

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Introduction

Renal tumors are the second most common abdominal tumors in children (0–14 years), following abdominal neuroblastomas. Wilms’ tumor (WT), an embryonal type of renal cancer also called nephroblastoma, is by far the most common renal neoplasm accounting for 85–95% of all pediatric renal malignancies 12345678 . While the incidence patterns of childhood WTs have been extensively studied [910] , less is known about the incidence of non-Wilms’ tumors (non-WT), which are infrequent in childhood representing approximately 10% of primary renal neoplasms and less than 1% of all childhood malignancies [81112] .

The diagnosis and thus estimation of incidence of non-WTs is challenging due to their rarity, the large heterogeneity of histological subtypes and their variable malignant potential [12] . In addition, incidence variations by age, gender and ethnicity have been reported for non-WTs [13] . The differential diagnosis of these tumors includes a large variety of epithelial, mesenchymal, neuroectodermal, and hematopoietic neoplasms [1415] , as well as benign disorders [16] . Of note is that non-neoplastic renal masses, such as hydronephrosis and multicystic dysplastic kidney should also be taken into consideration in the differential diagnosis, especially in certain age groups; i.e., only 20% of renal masses in the first year of life are true neoplasms [17] . The diagnosis of non-WTs can be suspected on the basis of their clinical and imaging features; however, radiology findings are not pathognomonic due to the non-specific morphology and the lack of specific radiological criteria [18] . Notably, in treatment centers where a tissue diagnosis is not a prerequisite to initiating treatment, misdiagnosis is possible and a significant proportion of patients may not receive optimal treatment, at least initially. Moreover, the rarity of this group of tumors poses additional challenges to the accurate diagnosis. Sociodemographic and clinical characteristics, such as the specific age distribution of each tumor subtype, the presence of nephroblastoma associated stigmata or genetic predisposition syndromes, the laboratory findings as well as the presence and the type of metastases can be helpful in the differential diagnosis [19] . Immunohistochemistry and molecular diagnostic approaches are nowadays mandatory to differentiate non-WTs and to establish a precise tissue diagnosis, but misdiagnosis may occur even in pathology reviews, including differences in initial histology and pathologic staging [3] . Discrepancies in risk stratification between pathology laboratories are identified in a substantial number of cases indicating the crucial contribution of central pathology review [2021] .

We aimed to estimate, for the first time in Greece, the incidence rates and trends of primary non-WTs overall and by histological subtype, as well as their distribution by demographic and clinical characteristics using data from the Nationwide Registry for Childhood Hematological Malignancies and Solid Tumors (NARECHEM-ST). We thereafter compared the data of malignant non-WT to those from the Surveillance, Epidemiology, and End Results Program (SEER), USA. The ratio of WT to non-WT in NARECHEM-ST, Greece was also calculated.