Primary peritoneal malignant mesothelioma (MM) can demonstrate morphologic overlap with low-grade and high-grade tubo-ovarian serous neoplasms; it is also biologically and prognostically distinct from benign mesothelial proliferations. Currently, there is no single biomarker that can definitively distinguish these neoplasms. Sex-determining region Y box 6 (SOX6) immunohistochemistry has been recently described to differentiate pleural epithelioid MM from lung adenocarcinoma, but it has not been evaluated in the peritoneum. SOX6 immunohistochemistry was performed on 43 peritoneal epithelioid MM, 7 peritoneal biphasic MM, 5 well-differentiated papillary mesotheliomas, 5 serous borderline tumors, 29 low-grade serous carcinomas (LGSCs), 20 high-grade serous carcinomas (HGSCs), and 25 cases of peritoneal reactive mesothelial hyperplasia. Quantitative SOX6 expression in epithelioid MM (median, 100% of tumor cells) was significantly greater than in LGSC/serous borderline tumor (median, 90%; P=0.004) and HGSC (median, 45%; P=0.0001). However, when SOX6 is expression is defined as ≥10% of tumor cells, there was no significant difference in the rate of SOX6 positivity between epithelioid MM (41/43, 95%), LGSC (28/29, 97%; P=1.0), and HGSC (17/20, 85%; P=0.16). Quantitative extent of SOX6 expression in epithelioid MM was significantly greater than in biphasic MM (median, 0%; P=0.0001), well-differentiated papillary mesothelioma (median, 20%; P=0.001), and reactive mesothelial hyperplasia (median, 20%; P=0.0001), but not significantly different from flat quiescent mesothelium (median, 90%; P=0.82). SOX6 immunohistochemistry is 95% sensitive for peritoneal epithelioid MM, but is also consistently expressed in LGSC and HGSC, negating its usefulness in this common differential diagnosis. SOX6 also shows variable expression across the spectrum of reactive, benign neoplastic, and malignant mesothelial lesions of the peritoneum, and does not appear to be diagnostically useful in distinguishing benign from malignant mesothelial proliferations.

原发性腹膜恶性间皮瘤（MM）可表现出与低级别和高级别输卵管卵巢浆液性肿瘤的形态重叠；它在生物学和预后上也与良性间皮增殖不同。目前，没有单一的生物标志物可以明确区分这些肿瘤。最近描述了性别决定区 Y 框 6 (SOX6)免疫组织化学可区分胸膜上皮样 MM 和肺腺癌，但尚未在腹膜中进行评估。对 43 例腹膜上皮样 MM、7 例腹膜双相性 MM、5 例高分化乳头状间皮瘤、5 例浆液性交界性肿瘤、29 例低级别浆液性癌（LGSC）、20 例高级别浆液性癌（HGSC）和 25 例进行 SOX6 免疫组化检查腹膜反应性间皮增生。上皮样 MM 中 SOX6 的定量表达（中位数，100% 肿瘤细胞）显着高于 LGSC/浆液性交界性肿瘤（中位数，90%；P = 0.004）和HGSC（中位数，45%；P = 0.0001）。然而，当SOX6表达定义为肿瘤细胞≥10%时，上皮样MM（41/43，95%）、LGSC（28/29，97%；P = 1.0）和 HGSC（17/20，85%；P =0.16）。上皮样 MM 中 SOX6 表达的定量程度显着大于双相 MM（中位数，0%；P = 0.0001）、分化良好的乳头状间皮瘤（中位数，20%；P = 0.001）和反应性间皮增生（中位数，20） %；P = 0.0001），但与平坦静止间皮没有显着差异（中位数，90%；P = 0.82）。SOX6免疫组织化学对腹膜上皮样 MM 的敏感性为 95%，但在 LGSC 和 HGSC 中也一致表达，从而否定了其在这种常见鉴别诊断中的用处。SOX6还在腹膜的反应性、良性肿瘤和恶性间皮病变范围内表现出不同的表达，并且在区分良性和恶性间皮增殖方面似乎没有诊断用处。