Myoepithelial carcinoma (MECA) is an underrecognized rare tumor with a diverse clinical behavior. The histologic features of this tumor are not well characterized, much less its grading, which is controversial. The objective of this study is to provide a better characterization of MECA and its prognostic factors. A total of 48 cases were retrieved from the pathology files. The cases were subjected to a detailed histopathologic, immunohistochemical, statistical, and clinical analysis. Tumors were classified as de novo MECA in 22 cases (46%) and carcinoma ex-pleomorphic adenoma (CA ex-PA) in 26 cases (54%). Tumor necrosis, high mitotic count (≥6/10 high-power fields), and severe pleomorphism were identified in 38%, 33%, and 21%, respectively. Perineural invasion, vascular invasion, and positive margins were noted in 10%, 12%, and 47%, respectively. Median follow-up was 38 months. Four patients had lymph node metastasis at presentation, 9 developed local recurrences, and 12 had distant metastases with the lung being the most common site (83%). The presence of CA ex-PA, necrosis, and vascular invasion correlated significantly with disease-free survival (P=0.02, 0.01, 0.03, respectively). No distant recurrence was noted in all 23 patients lacking necrosis in their neoplasms (median follow-up: 44 mo). MECA is a relatively aggressive tumor that is associated with a high rate of distant metastasis (27%). Compared with de novo MECA, CA ex-PA correlates with worse clinical outcome. A grading system based on the presence of tumor necrosis should be used to identify high-grade MECA and predict its clinical behavior.
肌上皮癌(MECA) 是一种认识不十分清楚的少见肿瘤，临床行为多变。该肿瘤的组织学特点不清楚，更不用说它的分级是矛盾的。研究目的在于更好地了解MECA 的特点和预后因素。
结果：肿瘤分为固有MECA 22例 (46%) 、癌在多形性腺瘤中(CA ex-PA)26例(54%)。肿瘤坏死、高核分裂指数 (≥6/10 hpf), 以及明显多形性的比率分别为38%, 33%, 21%。神经周围浸润、血管浸润和边缘阳性比率分别为10%, 12%, 47%。平均随访38个月。4例有淋巴结转移、 9例有局部复发，12 例有远处转移，最常见肺转移 (83%)。癌在多形性腺瘤中、坏死、血管浸润与无病生存明显相关(分别为P=0.02, 0.01, 0.03)。23例肿瘤中无坏死的病例无远处转移 （平均随访44 月）。
结论：MECA 为一种侵袭性明显的肿瘤，有较高的远处转移率 (27%)。与固有MECA相比，癌在多形性腺瘤中预后差。应把基于有无肿瘤性坏死的分级系统用于识别高级别MECA和它的临床行为。