Benign by definition means the tumor will not spread to distant locations or return later. Uterine fibroids are examples of benign tumors.
GIST should never be called benign as this is an misleading term. True enough some GISTs may never return. The problem is that doctors do not have a reliable test to determine which tumors will return and which ones probably won't. Therefore GISTs are rated not as benign or malignant but rather on a risk scale of low risk to high risk. Even small GISTs that looked "benign" have been known to act aggressively later.
GIST spreads by shedding GIST cells from the tumor into the blood stream, and these stray cells end up in locations like the liver. Just because a surgeon feels he has cut out all of the primary tumor with wide clear margins, he as no way to know if there are microscopic pockets of cells now deposited in the liver.
True enough not all GISTs ultimately behave as malignant. Because there are no ways to determine which ones will, a patient should consider her GIST as low risk rather than zero risk (benign). Low risk requires medical follow up for years to check for potential recurrence. We know of stores of people who went many many years before the disease returned--I have heard of one person who went 17 years after surgery for a "benign" GIST only later to have it return.
Good news is that low risk GISTs usually can be managed well with surgery, and pateints diagnosed with them tend to have about the same life span as those who were not diagnosed with GIST--even in the era before targeted therapy--There was a large retrospective Swedish study".
I think it is misleading to call GIST benign if it makes a patient believe that it was NON-cancer and never would have been cancer.... The trouble with the word "benign" is that it implies a difference in KIND rather than in quantity, like "Oh, it was not an apple, it was a grape."
Truly I agree that very tiny GISTs will not recur if removed. Does that mean they would be harmless if left in place to grow some more? Probably not, at least for those that do grow some more. (Some stop, but we do not know why.)
It is clear that some factors besides mutations must be present for large growth and the possibility of mets, but it is not clear to me from anything I have read just WHAT those factors are.
NCCN says all GISTs larger then 2 cm should be removed -- because they have malignant potential.
So my interpetation of calling a GIST benign (which I would not do myself) is that it means it had not YET metastasized when it was removed. That does not guarantee that the left-behind cells will not recur or metastasize in the future. Julie