Malignant peripheral nerve sheath tumor (MPNST) is a rare, often high-grade sarcoma. A small subset of MPNST shows evidence of heterologous rhabdomyoblastic differentiation, also known as malignant triton tumor (MTT). Immunohistochemical loss of histone 3 lysine 27 trimethylation (H3K27me3) has previously been described as a reliable marker for both MPNST and MTT.
To assess the loss of H3K27me3 as a potential tool for discriminating MTT from embryonal rhabdomyosarcoma (ERMS).
We studied the immunohistochemical expression of H3K27me3 in 23 pediatric cases of confirmed ERMS. Of the 23 patients, 21 were male and 2 were female, with an age range of 2 months to 18 years (median, 5 years). Most of the tumors arose in the paratesticular soft tissue (n = 14), with other locations including the pelvis (n = 3), thigh (n = 2), abdomen (n = 1), orbit (n = 1), prostate gland (n = 1), and parotid gland (n = 1). All cases had characteristic morphologic features of ERMS.
By immunohistochemistry, all tested cases expressed desmin (18 of 18), myogenin (20 of 20), and MyoD1 (5 of 5). More than half of the cases (12 of 23; 52%) showed loss (nuclear absence) of H3K27me3, defined as staining in less than 5% of the tumor cells. The remaining cases demonstrated some degree of partial staining with H3K27me3, ranging from 5 to 40% of the tumor cells. No significant correlation between H3K27me3 expression and clinicopathologic features was identified.
Loss of H3K27me3 frequently occurs in ERMS (52%) and is not reliable in distinguishing ERMS from MTT.
Author notes
The authors have no relevant financial interest in the products or companies described in this article.
Warmke and Davis contributed equally as first authors