CK7, along with cytokeratin 20 (CK20), is one of the most commonly used diagnostic antibodies for the determination of the origin of metastatic cancer tissues (Dum et al., 2022). CK7 and CK20 expression can be used as clinical parameters for the prognosis of different types of cancer. CK7 is usually negative in prostate and colorectal cancer, while CK7 positivity is indicative of urothelial origin or mucinous ovarian cancer. Aberrant expression of CK7 is associated with unfavorable tumor behavior. For example, Dum et al. (2022) correlated detectable expression of CK7 to unfavorable features in adenocarcinomas of the stomach, derived from CK7 negative precursor cells. In contrast, low expression of CK7 was linked to unfavorable features in breast cancer of no special type (NST) and urothelial carcinomas, both derived from CK7 positive precursor cells. In human lung cancer, CK7 positivity depends on the histological subtype (Johansson, 2004). Positive CK7 expression may be an independent clinical parameter for poor prognosis of lung cancer patients (Luo et al., 2017).