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Since the original description of pathogenic germline DICER1 variation underlying pleuropulmonary blastoma (PPB), the spectrum of extrapulmonary neoplasms known to be associated with DICER1 has continued to expand and now includes tumors of the ovary, thyroid, kidney, eye, and brain among other sites. This report documents our experience with another manifestation: a primitive sarcoma that resembles PPB and DICER1-associated sarcoma of the kidney. These tumors are distinguished by their unusual location in the peritoneal cavity, associated with visceral and/or parietal mesothelium. A total of seven cases were identified through pathology review in children presenting at a median age of 13 years (range 3-14 years). Primary sites of origin included the fallopian tube (four cases), serosal surface of the colon (one case), and pelvic sidewall (two cases). One case had pathologic features of type I PPB, another type Ir (regressed) PPB, and the remaining five had features of type II or III PPB with a mixed primitive sarcomatous pattern with or without cystic elements. All had a pathogenic DICER1 variation identified in germline and/or tumor DNA. PPB-like peritoneal tumors represent a newly described manifestation of DICER1 pathogenic variation whose pathologic features are also recapitulated in DICER1-related renal sarcoma, cervical embryonal rhabdomyosarcoma, and some Sertoli-Leydig cell tumors with heterologous elements. Tumors arising from the fallopian tube or elsewhere in the abdomen/pelvis, especially those with heterogeneous rhabdomyosarcomatous and/or cartilaginous differentiation, should prompt consideration of germline and tumor DICER1 testing.

Embryonal rhabdomyosarcoma (ERMS) is the most common childhood sarcoma and is a component of the familial pleuropulmonary blastoma (PPB)-predisposition syndrome. Using the PPB model, we hypothesized that DICER1 mutations would be found in familial and sporadic forms of ERMS. Blood samples from four children with familial PPB and ERMS, and 52 sporadic ERMS tumors were tested for DICER1 mutations. Germline DICER1 mutations were found in all four patients with familial PPB and 2 of 52 (3.8%) sporadic ERMS had somatic mutations. Our findings confirm the pathogenetic relationship between ERMS and PPB suggesting that ERMS may result from abnormal miRNA regulation., (Copyright © 2011 Wiley Periodicals, Inc.)

Pleuropulmonary blastoma (PPB) is a rare pediatric lung tumor that is often part of an inherited cancer syndrome. PPBs consist of mesenchymal cells that are susceptible to malignant transformation and cysts lined by epithelial cells. In a subset of patients, overgrowth of the cysts by mesenchymal cells leads to sarcoma formation. Here, we show that 11 multiplex PPB families harbor heterozygous germline mutations in DICER1, a gene encoding an endoribonuclease critical to the generation of small noncoding regulatory RNAs. Expression of DICER1 protein was undetectable in the epithelial component of PPB tumors but was retained in the malignant mesenchyme (sarcoma). We hypothesize that loss of DICER1 in the epithelium of the developing lung alters the regulation of diffusible factors that promote mesenchymal proliferation.