It is not a question of the test being or not Good enough, it depends on the population. Even 99% S/S tests when applied to a population with very low risk of being sick will result in false conclusions. That’s why we must consider the “pre-test probability”, which is basically the presumed prevalence. If you take a pregnancy test and use it in young females sexually active with their periods delayed, and then use the same test in nuns with regular periods, the accuracy will be very different.

Some of them as injected inside or nearby the tumor, that by itself makes things easier. Other thing is that some of these viruses are genetically modified in such a way that they need a certain apparatus to multiply that only tumor cells have, such as a higher metabolism and a higher multiplication rate - and therefore different amount of organeles and different signaling pathways