As time has gone on and the medical field has become more and more experienced, so has cancer research evolved as well. There have been many improvements made, and nowadays you can catch cancer in its early stages much more frequently than it was done even a decade ago. Despite this, there are still a lot of early stage cancers that are very hard to detect.
This can happen not only due to the fact that they are in places that are hard to see on normal screenings, but also because they end up giving the patient symptoms or showing signs only when the disease has evolved past its initial stages. When tumors have reached an advanced stage in most of these hard to detect cancers, they can not only be extremely hard to remove, but they can end up spreading around to neighboring organs as well, making tackling them even more difficult.