Since the original description of pathogenic germline DICER1 variation underlying 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 to 14 years). Primary sites of origin included the Fallopian tube (4 cases), serosal surface of the colon (one case), and pelvic sidewall (2 cases). One case had pathologic features of type I PPB, another type Ir (regressed) PPB and the remaining 5 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.

Granulomatous lung disease is a rare and perplexing differential in pediatrics. Pulmonary Cryptococcus falls into the differential but is not high on the list, particularly in a non-AIDS patient. Methotrexate (MTX) is a commonly used agent for chemotherapy in oncology and has been documented to cause lung injury in both patients with rheumatologic and oncologic diseases. Our patient had chronic cough and then developed an opportunistic infection resulting in respiratory failure. Lung biopsy showed two underlying unusual diagnoses: MTX lung injury and cryptococcal pneumonia. His case is presented with particular attention to his prolonged road to diagnosis.

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