Why is miR-15b-5p listed as 'internal control only' and not a cancer marker?

miR-15b-5p is included in the Yenos assay for quality control, not cancer detection. It is a miRNA whose expression level is not expected to change between healthy and cancer populations — it is constitutively expressed at a stable level in most cell types. Because its level should remain constant regardless of cancer status, any deviation from the expected level in a patient sample signals a technical problem: the extraction may have failed, the nanopore run may have been disrupted, or the sample may have degraded. If miR-15b-5p is out of range, the result is withheld and the sample is flagged for re-analysis. This is why miR-15b-5p is emphatically NOT a cancer biomarker — calling it a cancer marker would be scientifically incorrect and misleading.