Metachronous anaplastic sarcoma of the kidney and thyroid follicular carcinoma as manifestations of DICER1 abnormalities.

Anaplastic sarcoma of the kidney (ASK) is a tumor found in the pediatric age group and shows many histopathological similarities to pleuropulmonary blastoma (PPB). We present a 12-year-old girl diagnosed with ASK and, 3 years later, with thyroid follicular carcinoma (TFC) with DICER1 abnormalities. Germline insertion/deletion (p. G1809_S1814delinsA) and independent somatic mutations (p. E1705K in ASK, p. E1813D in TFC) were identified. All of these abnormalities are in the catalytic domain of RNase IIIb. Single-nucleotide polymorphism genotyping microarray revealed independent copy number alterations (trisomy 8, monosomy 10, loss of 17p, and partial gain of 17q in ASK; trisomy 5 and partial loss of Xq in TFC). The copy number alteration pattern of ASK was similar to the pattern previously reported in PPB. The present case implies that ASK is a renal counterpart of PPB and that ASK with DICER1 abnormalities should be suspected in a broader age group than PPB.