SPDEF and prostate cancer: Based on studies of intracellular mRNAs, two successful commercial kits use urinary exosomal mRNAs (SAM pointed domain-containing ETS transcription factor (SPDEF) and ETS transcription factor (ERG)) and plasma exosomal mRNA (echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion transcripts) to detect prostate cancer and nonsmall-cell lung cancer, respectively [50,51,52], which demonstrates the functionality of exosomal mRNAs as biomarkers.