Response to Lee et al: Toward a unifying entity that encompasses most, but perhaps not all, inflammatory leiomyosarcomas and histiocyte-rich rhabdomyoblastic tumors

To the Editor:

We thank Drs. Lee and colleagues for their interest in our recent study [1] and for sharing their own very informative data [2]. Certainly their cases seem to show essentially identical clinical, morphologic, immunohistochemical and molecular genetic features to those previously reported, and add to our collective understanding of inflammatory rhabdomyoblastic tumor. As the authors suggest, FISH may represent an alternative technique for the diagnosis of these tumors in centers lacking the OncoScan assay, or another SNP array test.

Unquestionably, the best characterized subset of inflammatory rhabdomyoblastic tumors are those displaying the near-haploid karyotype, with retained disomy of 5 and 22, and it seems quite clear that these tumors represent rhabdomyoblastic tumors of borderline malignancy with low metastatic risk, and some risk of progression to conventional rhabdomyosarcoma (as described in our own accompanying letter). The natural history and relationship of those inflammatory rhabdomyoblastic tumors with a diploid karyotype needs further study, given their rarity. As discussed in our study, there also seem to be other tumors showing smooth muscle differentiation and having a prominent inflammatory cell infiltrate, which likely represent other sarcoma types.