Objective: To investigate the clinicopathological features, diagnosis and differential diagnosis of breast myofibroblastoma. Methods: The clinicopathological data and prognostic information of 15 patients with breast myofibroblastoma diagnosed at the Department of Pathology of the First Affiliated Hospital of Zhengzhou University, Zhengzhou, China from 2014 to 2022 were collected. Their clinical characteristics, histological subtypes, immunophenotypes and molecular characteristics were analyzed. Results: There were 12 female and 3 male patients, ranging in age from 18 to 78 years, with a median and average age of 52 years. There were 6 cases in the left breast and 9 cases in the right breast, including 12 cases in outer upper quadrant, 2 cases in inner upper quadrant and 1 case in outer lower quadrant. Most of the cases showed a well-defined nodule grossly, including pushing growth under the microscope in 13 cases, being completely separated from the surrounding breast tissue in 1 case, and infiltrating growth in 1 case. Among them, 12 cases were classic subtype and composed of occasional spindle cells with varying intervals of collagen fiber bundles; eight cases had a small amount of fat; one case had focal cartilage differentiation; one case was epithelioid subtype, in which epithelioid tumor cells were scattered in single filing or small clusters; one case was schwannoma-like subtype, and the tumor cells were arranged in a significant palisade shape, resembling schwannoma, and one case was invasive leiomyoma-like subtype, in which the tumor cells had eosinophilic cytoplasm and were arranged in bundles, and infiltrating into the surrounding mammary lobules like leiomyoma. Immunohistochemical studies showed that the tumor cells expressed desmin (14/15) and CD34 (14/15), as well as ER (15/15) and PR (15/15). Three cases with histologic subtypes of epithelioid subtype, schwannoma-like subtype and infiltrating leiomyoma-like subtype showed RB1 negative immunohistochemistry. Then FISH was performed to detect RB1/13q14 gene deletion, and identified RB1 gene deletion in all three cases. Fifteen cases were followed up for 2-100 months, and no recurrence was noted. Conclusions: Myofibroblastoma is a rare benign mesenchymal tumor of the breast. In addition to the classic type, there are many histological variants, among which the epithelioid subtype is easily confused with invasive lobular carcinoma. The schwannoma-like subtype is similar to schwannoma, while the invasive subtype is easily misdiagnosed as fibromatosis-like or spindle cell metaplastic carcinoma. Therefore, it is important to recognize the various histological subtypes and clinicopathological features of the tumor for making correct pathological diagnosis and rational clinical treatment.
目的： 探讨乳腺肌纤维母细胞瘤的临床病理特征、诊断及鉴别诊断。 方法： 收集2014—2022年郑州大学第一附属医院病理科诊断的乳腺肌纤维母细胞瘤15例患者的临床病理资料及预后信息，分析其临床特点、组织学亚型、免疫表型及分子学特征。 结果： 15例患者女性12例，男性3例，年龄18~78岁，中位与平均年龄均为52岁。发生于左乳6例，右乳9例，其中外上象限12例，内上象限2例，外下象限1例。大体上多数表现为界限清楚的结节，其中镜下呈推挤式生长的有13例，与周围乳腺组织截然分开的有1例，另外1例呈浸润性生长。其中12例为经典亚型，肿瘤由温和的梭形细胞间隔多少不等的胶原纤维束组成，其中8例伴有少量脂肪成分，1例局灶伴有软骨分化，1例为上皮样亚型，上皮样肿瘤细胞呈散在单个/单行或小簇状分布，1例为神经鞘瘤样亚型，肿瘤细胞呈显著的栅栏状排列，非常类似于神经鞘瘤，1例为浸润性平滑肌瘤样型，肿瘤细胞胞质红染，呈束状排列，似平滑肌瘤样形态向周围乳腺小叶间呈浸润性生长。免疫组织化学结果显示肿瘤细胞表达结蛋白（14/15）和CD34（14/15），并表达雌激素受体（15/15）、孕激素受体（15/15），其中组织学亚型分别为上皮样亚型、神经鞘瘤样亚型及浸润性平滑肌瘤样亚型的3例均显示免疫组织化学RB1阴性，随后行荧光原位杂交检测RB1/13q14基因缺失情况，结果显示3例均存在RB1基因缺失。15例随访时间2~100个月，均未复发。 结论： 乳腺肌纤维母细胞瘤是一种罕见的乳腺良性间叶源性肿瘤，除经典型外，尚有多种组织学变异型，其中上皮样亚型易与浸润性小叶癌相混淆，神经鞘瘤样亚型酷似神经鞘瘤，浸润性亚型易误诊为纤维瘤病样或梭形细胞化生性癌等，认识该肿瘤不同组织学亚型及其临床病理学特征对诊断及治疗具有重要意义。.