Recurrent EGFR alterations in NTRK3 fusion negative congenital mesoblastic nephroma

OBJECTIVES: To identify oncogenic driver mutations in congenital mesoblastic nephroma (CMN) cases lacking ETV6-NTRK3 fusion and discuss their diagnostic value. DESIGN: The institutional pathology database was queried for cases with a morphologic diagnosis of CMN. Cases positive for ETV6 rearrangement or with unavailable blocks were excluded. Four cases met the inclusion criteria and were sequenced by next-generation sequencing. Three additional cases were contributed by our collaborators. RESULTS: Three of four internal cases harbor an EGFR kinase domain duplication (KDD), which is known to be oncogenic yet exceedingly rare in other histologies. All three outside cases are positive for EGFR alterations, including KDD in two and a splicing site mutation in one. The splicing site mutation is predicted to be EGFR activating. One of the outside cases was a retroperitoneal mass without a clear site of origin. A diagnosis of CMN is suggested based on exclusion of differential diagnoses by expert consultation and detection of EGFR KDD. CONCLUSIONS: EGFR activation, predominantly via EGFR KDD, is a common recurrent genetic alteration in CMN lacking NTRK3 fusions. CMN can be molecularly classified into NTRK3 fusion type, EGFR activation type and others.