KRT7 and small cell carcinoma: In one report, a patient with lung cancer presented with a metastatic nodule on their neck that was CK7−/CK20+, leading to the diagnosis of small cell neuroendocrine carcinoma; however, postmortem analysis showed that the primary tumor was a small cell lung carcinoma that was CK7+/CK20−, suggesting that the CK expression profile switched during metastatic disease progression [60].