Field cancerization may be an extended form of the Knudson hypothesis. This is the phenomenon of various primary tumors developing in one particular area of the body, suggesting that an earlier "hit" predisposed the whole area for cancer. Announced in 2011,
chromothripsis similarly involves multiple mutations, but asserts that they may all appear at once. This idea, affecting only 2–3% of cases of cancer, although up to 25% of bone cancers, involves the catastrophic shattering of a
chromosome into tens or hundreds of pieces and then being patched back together incorrectly. This shattering, it is presumed, takes place when the chromosomes are compacted during
normal cell division, but the trigger for the shattering is unknown. Under this model, cancer arises as the result of a single, isolated event, rather than the slow accumulation of multiple mutations. The exact function of some tumor suppressor genes is not currently known (e.g.
MEN1,
WT1), but based on these genes following the Knudson "two-hit" hypothesis, they are strongly presumed to be suppressor genes. ==References==