Abstract：
Primary mucinous cystadenocarcinoma (MCA) of the breast is a rare variant of breast carcinoma. A 68-year-old female patient presented to the general surgery clinic with pain and swelling in the right breast. A mass was detected in the upper outer quadrant, and a fine-needle aspiration biopsy was performed. The May-Grünwald Giemsa stained slides showed aggregates of mucin-rich pleomorphic cells with large nuclei in a mucinous background containing discohesive single cells. The Papanicolaou stain revealed a papillary structure composed of malignant epithelial cells in a necrotic background. A modified radical mastectomy was performed, and upon gross examination, two tumors were discovered in the central and upper outer quadrants. The first tumor, located centrally, was identified as invasive lobular breast carcinoma. The second tumor was an MCA with cytokeratin 7(+) and cytokeratin 20(-), and was determined to be the primary MCA of the breast based on clinical and radiological information. Immunohistochemistry revealed that the tumor cells were negative for estrogen receptor and progesterone receptor, and HER2 was 2+. Fluorescence in situ hybridization analysis detected HER2 gene amplification. During the 72-month follow-up, there were no findings compatible with recurrence or new metastasis. Although primary MCA is rare, it causes differential diagnosis problems and has different biological behaviors.
摘要：
乳腺原发性粘液性囊腺癌（MCA）是乳腺癌的罕见变体。一名68岁的女性患者出现在普外科诊所，右乳房疼痛和肿胀。在上部外象限检测到肿块，并进行了细针穿刺活检。May-GrünwaldGiemsa染色的载玻片显示，富含粘蛋白的多形性细胞聚集，在粘液性背景中具有大的细胞核，其中包含盘状单细胞。Papanicolaou染色显示出由坏死背景下的恶性上皮细胞组成的乳头状结构。进行了改良根治术,经过粗略检查，在中央和上外侧象限发现了两个肿瘤。第一个肿瘤,位于中央,被确定为浸润性小叶乳腺癌。第二个肿瘤是具有细胞角蛋白7（+）和细胞角蛋白20（-）的MCA，根据临床和放射学信息确定为乳腺的主要MCA。免疫组织化学显示肿瘤细胞雌激素受体和孕激素受体阴性，HER2为2+。荧光原位杂交剖析检测到HER2基因扩增。在72个月的随访中，没有发现与复发或新转移相符.虽然初级MCA很少见，它引起鉴别诊断问题并具有不同的生物学行为。
