Aims
Myeloid sarcoma (MS) is a rare extramedullary neoplasm composed of immature myeloid precursor cells thought to be a unique clinical presentation of acute myeloid leukaemia (AML). Like AML, MS has a poor prognosis, but due to the rare nature of MS there are limited studies examining potential prognostic factors. We report our institutional experience, with the aim of investigating and establishing salient clinicopathological and molecular features of MS.
Methods and results
We retrospectively examined all clinicopathological and molecular data on MS patients between 2001 and 2017 from the University of Alabama at Birmingham (UAB) electronic medical records. The UAB electronic medical records were also reviewed and compared with the literature for other potential prognostic factors. Sixty‐three patients were included in the study. The median overall survival was 24 months in the group with normal karyotype and 12 months in patients with an abnormal karyotype.
Conclusions
We found that an abnormal karyotype was associated with a statistically significant worse prognosis.
PAX8 is used as a diagnostic aid in classifying retroperitoneal (RP) spindle cell tumors. PAX8 positivity in a spindled RP tumor is typically associated with sarcomatoid renal cell carcinoma (SRCC). However, PAX8 expression in solitary fibrous tumor (SFT), a tumor not uncommon to the RP, has not been extensively studied. We investigated the expression of PAX8 in SFTs and other spindle cell RP tumors. We collected 30 SFT, 23 SRCC, 11 gastrointestinal stromal tumors, 2 synovial sarcomas, 6 dedifferentiated liposarcomas (DDLS), 4 well differentiated liposarcomas (WDLS), and select other tumors. We identified nuclear PAX8 expression in 13 of 30 (43%) SFT, 0 of 6 (0%) DDLS, and 1 of 4 (25%) WDLS. Twenty-eight of 30 (93%) SFT, 0 of 23 (0%) SRCC, 2 of 6 (33%) DDLS, and 1 of 4 (25%) WDLS showed nuclear STAT6 expression. All gastrointestinal stromal tumors were negative for both PAX8 and STAT6. Of the 13 SFT showing PAX8 expression, 8 showed diffuse expression and 5 expressed PAX8 focally. Extrapleural SFTs were more likely to express PAX8 compared with pleural SFTs (10/13; 77% vs. 3/17; 18%, respectively; P=0.00117). Twenty of 23 (87%) SRCC expressed PAX8; the sarcomatoid component of all 23 SRCC was negative for STAT6. Of the other spindle cell tumors studied, 1 of 2 synovial sarcomas and 1 of 2 histiocytic sarcomas showed PAX8 expression. Pathologists should be aware of the potential pitfall of the relatively frequent expression of PAX8 by SFT and STAT6 expression in liposarcoma. PAX8 expression by a spindle cell lesion of RP would not allow distinction between SFT, SRCC, or sclerosing liposarcoma by itself. A STAT6/PAX8 phenotype excludes SRCC.
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