Decrease of TET2 expression and increase of 5-hmC levels in myeloid sarcomas.

BACKGROUND

Myeloid sarcoma is a tumor mass that consists of myeloblasts or immature myeloid cells at an extramedullary site. Pathological diagnosis is very difficult based on morphology if systemic signs of disease are absent. The subtype of myeloid sarcoma is also minimally identifiable in the histological picture.

FINDINGS: We investigated 18 paraffin-embedded myeloid sarcoma samples, and our immunohistochemical data confirmed the relevance of some key markers for the diagnosis and subclassification of myeloid sarcoma. CD34 was found as a marker in 67% of the myeloid sarcoma cases, and CD34 was positive in all immature types of myeloid sarcoma. CD68 was found in 83% of the myeloid sarcoma cases, but CD68 was most identified in the differentiated type of myeloid sarcoma. Myeloperoxidase (MPO) was positive in all myeloid sarcomas. Notably, the reactivity of MPO in the blastic subtype was much lower in myeloid sarcomas. CD117 reactivity was found in 67% of myeloid sarcomas. Ten-eleven translocation 2 (TET2) protein exhibited significant negative reactivity in 88% of the cases, and 5-methylcytosine (5-hmC) was significantly positive in the nucleus in 100% of the cases.

CONCLUSIONS

Our findings indicated that an immunohistochemical panel that included MPO, CD68 and CD34 could be used for the detection of blastic, differentiated and immature types of myeloid sarcoma. Changes in novel epigenetic regulators, including the loss of TET2 and gain of 5-hmC, as characteristics of myeloid malignancies may be useful novel markers of myeloid sarcoma.