Premium
PAX 7 immunohistochemical evaluation of Ewing sarcoma and other small round cell tumours
Author(s) -
Toki Shunichi,
Wakai Susumu,
Sekimizu Masaya,
Mori Taisuke,
Ichikawa Hitoshi,
Kawai Akira,
Yoshida Akihiko
Publication year - 2018
Publication title -
histopathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.626
H-Index - 124
eISSN - 1365-2559
pISSN - 0309-0167
DOI - 10.1111/his.13689
Subject(s) - sarcoma , synovial sarcoma , immunohistochemistry , pathology , rhabdomyosarcoma , alveolar rhabdomyosarcoma , ewing's sarcoma , desmoplastic small round cell tumor , tissue microarray , biology , osteosarcoma , embryonal rhabdomyosarcoma , medicine
Aims Ewing sarcoma is a small round cell tumour that affects bone and soft tissues. Although the detection of the specific fusion gene is a robust method of its diagnosis, immunohistochemistry may serve as a practical surrogate. Recent tissue microarray studies suggested that PAX 7 is a novel marker, because it was expressed consistently in Ewing sarcoma, in addition to rhabdomyosarcoma and synovial sarcoma. Here, we evaluated the utility of PAX 7 immunohistochemistry in whole‐tissue sections of an expanded array of round cell malignancies with adequate molecular characterisation. Methods and results We stained 30 molecularly confirmed Ewing sarcomas, one EWSR 1– NFATC 2 sarcoma and 141 non‐Ewing round cell tumours by a monoclonal antibody against PAX 7. Staining was considered positive if at least 5% of tumour cells were stained. PAX 7 was expressed in 27 of 30 Ewing sarcomas (90%), mainly in a diffuse and strong manner. Although NKX 2‐2 showed similar sensitivity, PAX 7 showed more extensive and strong reactivity. One EWSR 1– NFATC 2 sarcoma co‐expressed PAX 7 and NKX 2‐2. PAX 7 was also expressed in 24 of 141 non‐Ewing tumours, including alveolar rhabdomyosarcomas (seven of 10), poorly differentiated synovial sarcomas (seven of 10), BCOR – CCNB 3 sarcomas (eight of 10), small‐cell osteosarcoma (one of five) and desmoplastic small round cell tumour (one of 10), one‐third of which showed diffuse strong reactivity. Conclusions Although we confirmed that PAX 7 is a sensitive marker for Ewing sarcoma, anti‐ PAX 7 antibody also stained several Ewing sarcoma mimics, whose spectrum was distinct from NKX 2‐2‐positive non‐Ewing entities. Further studies are required to determine how PAX 7 could be integrated into practice to classify small round cell tumours efficiently.