For patient No.2, we compared CNAs of two CTCs and CD56‐positive SCNEC cells as well as glandular HER2‐positive single tumoroids to discriminate whether the SCNEC cells were derived from an independent metachronous small cell lung cancer or if they were the result of near complete loss of differentiation of the adenoid cystic salivary gland carcinoma. Here, NCAM1 is linked to small cell lung carcinoma.