Why do you believe many cancers go unrecognized until after the formation of tumors and/or the person becomes

Some cancers go unrecognised because they tend not to grow in a steady, linear order. These tumors can remain dormant for long periods of time unless triggered by a promoter agent that will promote its growth followed by a period of rapid and fast growth, such as occurs after angiogenesis is initiated. Thus, equipment that will be extremely sensitive to the processes that these cells before they metastasize has to be developed to detect their presence. Some available equipments detect their actions through the substances they shed into the bloodstream but these cells would have begun metastasis by this period.