Why isn't the sensitivity 100% — why does miR-375 only achieve 81.5%?

No screening test achieves 100% sensitivity — there will always be some cases where a cancer patient's miRNA expression does not rise above the detection threshold at the time of testing. For miR-375, the 81.5% sensitivity reflects biological variation: not all cancer types overexpress miR-375 to the same degree, and in some patients, miR-375 may not be the primary dysregulated marker. This is exactly why OncuraKit measures three independent markers: a patient who is negative on miR-375 may still be positive on miR-21 (93.8% sensitivity) or miR-141 (97.3%). The combined panel approach and the availability of a confirmatory second test ensure that the overall test sensitivity and specificity are maximized. Using all three markers together, the probability of missing a true cancer is substantially lower than using any single marker alone.