Distant metastasis from salivary gland secretory carcinoma (SC) is rare, with lung and pleura being the most frequent site. While cytological features of SC on fine needle aspirates are well documented, its morphology in serous effusions has not been described. We describe the cytomorphological features on effusion cytology of two patients with ETV6::NTRK3 fusion-positive SC, who subsequently developed pleural metastases. Cytospin preparations of pleural fluid showed tightly cohesive, irregularly shaped and ball-like clusters of large tumor cells with scant to abundant uni- and multi-vacuolated cytoplasm. Nuclei were eccentrically placed, round to oval, vesicular, with finely granular chromatin, irregular nuclear membranes and conspicuous to prominent nucleoli. With these features, the tumors resembled an adenocarcinoma, indistinguishable from a lung primary. Cell blocks from both cases showed tumor fragments, some of which had the hollow appearance of transversely sectioned cell spheres as seen in lung and breast adenocarcinomas. Immunohistochemistry on cell blocks revealed nuclear pan-TRK positivity in both cases. Case 1 also showed focal mammaglobin staining, and TTF1 negativity. Pleural metastases from SC may mimic other adenocarcinomas. As targeted therapy, that is, selective TRK inhibitors are available for treatment of metastatic disease, NTRK3 fusion status is not only diagnostic, but also required to plan treatment. Pan-TRK immunohistochemistry serves as a viable cost-effective, easy to apply surrogate marker for NTRK3 fusion, particularly in diagnostic laboratories lacking easy access to molecular testing on cytological material.

中文翻译：

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腮腺分泌性癌的胸膜转移：渗出液细胞学形态学的首次报告，以及泛 TRK 免疫组织化学的作用

唾液腺分泌性癌 (SC) 的远处转移很少见，肺和胸膜是最常见的部位。虽然 SC 在细针穿刺中的细胞学特征已得到充分记录，但其在浆液性积液中的形态学尚未得到描述。我们描述了两名ETV6::NTRK3患者的渗出细胞学细胞形态学特征融合阳性 SC，随后发生胸膜转移。胸腔积液的细胞离心涂片标本显示紧密结合、形状不规则和球状的大肿瘤细胞簇，具有少量至丰富的单空泡和多空泡细胞质。细胞核偏心排列，圆形至椭圆形，呈水泡状，染色质呈细颗粒状，核膜不规则，核仁明显至突出。具有这些特征，肿瘤类似于腺癌，与肺原发性无法区分。两种情况下的细胞块均显示肿瘤碎片，其中一些具有横切细胞球的空心外观，如肺腺癌和乳腺癌中所见。细胞块的免疫组织化学显示两种情况下的核泛 TRK 阳性。案例 1 还显示局灶性乳房珠蛋白染色和 TTF1 阴性。SC 的胸膜转移可能类似于其他腺癌。作为靶向治疗，即选择性TRK抑制剂可用于治疗转移性疾病，NTRK3融合状态不仅是诊断，也是制定治疗计划所必需的。Pan-TRK 免疫组织化学可作为一种可行的具有成本效益、易于应用的NTRK3融合替代标记，特别是在缺乏对细胞学材料进行分子检测的诊断实验室中。