Comment on: “Indications and results of diagnostic biopsy in pediatric renal tumors: A retrospective analysis of 317 patients with critical review of SIOP guidelines”

We read with interest the article by de la Monneraye et al on the experience of the Institut Curie of renal tumor biopsy in children treated according to SIOP protocols over a 22-year period.1 By presenting the relative proportion of children with non-Wilms tumorswhohad clinical, radiological, and biochemical features that are considered “atypical” of Wilms tumors (WT), they support a change to an evidence-based approach to biopsy in the SIOP community. However, some of their recommendations are not adequately supported by a single institutional series, and we would like to add some reflections from our work based on the nationaland population-level data. First, they rightly identify that if age alone is the criterion to biopsy to identify non-WT, then six years is an inappropriately low cutoff. They are also right that biopsy could be considered for infants between 3 and 6 months, as in this age group, benign tumors are a minority of cases in their series and others.2–4 However, raising the upper age criterion to nine years is taken from a figure where they have grouped 9–12 years together—why not choose 10, 11, or 12 years? Comparing tumor distribution among the incident population, rather than a single institution's referral practice, is more accurate. Based on English National Cancer Registry data from 2006 to 2015, the age of the inflection point when WT changes from 83% to 38% of pediatric renal tumors is from 10 to 11 years.2 On this basis, we suggest an age of 10 years and older as a cutoff.2 Second, they state that upfront surgery should be considered for children with small volume tumors as “chemoreduction” is unnecessary. However, tumor size is not necessarily related to risk of tumor rupture. Childrenwhowere not randomized in theUKW3 trial and had elective immediate nephrectomy had smaller median tumor size and yet had significantly higher rupture rates than thosewho received preoperative therapy.5 Furthermore, preoperative chemotherapy allows for stratification based on chemoresponsiveness irrespective of reducing rupture risk. Third, their claim in the discussion that a large tumor volume discriminates between WT and non-WT after adjustment for age is not supported by appropriate statistical analysis. The distribution of tumor volumes in Fig. 2 shows both clear cell sarcoma of the kidney and WT may be large (>500 mL) at presentation. Clearly a larger study, better powered to identify any potential volume threshold, is needed. Fourth, they overstate the utility of fine needle aspirates to replace or adjunct cutting needle biopsy. Biopsy type does not determine the possible genetic analyses; necrotic samples are rare if image guidance is used; coagulopathy is a contraindication for any biopsy using a coaxial technique and their cited study of adult practice is underpowered and not obviously applicable to a pediatric context. Finally, two errata. (1) Vujanic et al6 report the incidence of specific complications from 0.5% to 20% not a total complication rate of 1.2% as cited; (2) Irtan et al (reference 61) should be attributed for the analysis of relapse risk after biopsy in the UKW3 trial, not reference 62.