Keratins are essential elements of the cytoskeleton of normal and malignant epithelial cells. Because carcinomas commonly maintain their specific keratin expression pattern during malignant transformation, keratins are extensively used as tumor markers in cancer diagnosis including the detection of circulating tumor cells in blood of carcinoma patients. Interestingly, recent biological insights demonstrate that epithelial keratins should not only be considered as mere tumor markers. Emerging evidence suggests an active biological role of keratins in tumor cell dissemination and metastasis. In this review, we illustrate the family of keratin proteins, summarize the latest biological insights into keratin function related to cancer metastasis and discuss the current use of keratins for detection of CTCs and other blood biomarkers used in oncology.

角蛋白是正常和恶性上皮细胞的细胞骨架的基本要素。由于癌通常在恶性转化期间维持其特定的角蛋白表达模式，因此角蛋白被广泛用作癌症诊断中的肿瘤标志物，包括检测癌症患者血液中循环的肿瘤细胞。有趣的是，最近的生物学见解表明，上皮角蛋白不仅应被视为单纯的肿瘤标志物。新兴证据表明角蛋白在肿瘤细胞的传播和转移中具有积极的生物学作用。在这篇综述中，我们举例说明了角蛋白家族，总结了与癌症转移相关的角蛋白功能的最新生物学见解，并讨论了角蛋白在检测肿瘤中使用的CTC和其他血液生物标记物中的用途。