MVP immunohistochemistry is a useful adjunct in distinguishing leiomyosarcoma from leiomyoma and leiomyoma with bizarre nuclei

Morphologically, distinguishing between leiomyoma (LM) and leiomyosarcoma (LMS) is not always straightforward, especially with benign variants such as bizarre leiomyoma (BLM). To identify potential markers of malignancy in uterine smooth muscle tumors, proteomic studies were performed followed by assessment of protein expression by immunohistochemistry. Archival formalin-fixed, paraffin-embedded tissues from tumors (n = 23) diagnosed as LM, BLM, and LMS (using published criteria) were selected for the study. Sequential window acquisition of all theoretical fragment ion spectra mass spectrometry was applied to pooled samples of formalin-fixed, paraffin-embedded LM and LMS tumor tissue to assay the relative protein quantities and look for expression patterns differentiating the 2 tumor types. A total of 592 proteins were quantified, and 10 proteins were differentially expressed between LM and LMS. Select proteins were chosen for evaluation by immunohistochemistry (IHC) based on antibody availability and biologic relevance in the literature. IHC was performed on a tissue microarray, and intensity was evaluated using imaging software. Major vault protein (MVP) and catechol O-methyltransferase had 3.05 and 13.94 times higher expression in LMS relative to LM by sequential window acquisition of all theoretical fragment ion spectra mass spectrometry, respectively. By IHC, MVP (clone 1014; Santa Cruz Biotechnology, Dallas, TX) was found to be 50% sensitive and 100% specific when comparing LMS to LM. Catechol O-methyltransferase (clone FL-271; Santa Cruz Biotechnology) had a sensitivity of 38% and a specificity of 88%. Six of 7 BLM had expression of MVP similar to LM. Immunohistochemical staining for MVP is a useful adjunct in distinguishing LMS from LM and BLM in difficult cases.