Notably, tissue testing may still be indicated specifically in cases where transformation of cancer to a different histology is a concern, for example, small cell transformation of EGFR-mutated NSCLC after treatment with tyrosine kinase inhibitors [43] or prostate adenocarcinoma into small cell neuroendocrine cancer under androgen deprivation therapy [44]. Here, EGFR is linked to non-small cell lung carcinoma.