Gastrointestinal Stromal Tumours (GISTs) with KRAS Mutation: A Rare but Important Subset of GISTs

Table 1

Immunohistochemical molecular scenarios in gastrointestinal stromal tumours (GISTs).

Scenarios	% of GIST	Immunohistochemistry			Molecular
		KIT	DOG1	SDHB	KIT	PDGFRα	SDH	BRAF	NF1	Other
(i) Usual GIST	85–90%	Pos	Pos	Retained	Mutated	Mutated	Wt	Wt	Wt	Wt
(ii) KIT/PDGFRαSDH-deficient GIST	10–15%	Pos	Pos	Lost	Wt	Wt	Mutated or methylated	Wt	Wt	Wt
(iii) KIT/PDGFRα/SDH GIST	1-2%	Pos	Pos	Retained	Wt	Wt	Wt	Mutated	Mutated	Wt
(iv) KIT/PDGFRα/SDH GIST	<1%	Pos	Pos	Retained	Wt	Wt	Wt	Wt	Wt	KRAS/PIK3C/NTRK/FGFR etc. mutated
(v)	<1%	Neg	Neg	Retained	Mutated	Mutated	Wt	Wt	Wt	Wt
(vi)	Rare	Neg	Pos	Retained	Wt	Mutated	Wt	Wt	Wt	Wt
(vii)	Very rare	Neg	Neg	Retained	Wt	Wt	Wt	Wt	Wt	Wt

Pos = positive; Neg = negative; Wt = wild type;  = KIT or PDGFRα is mutated = BRAF or NF1 is mutated;  = this is a very rare scenario, and all tests should be repeated. Consideration whether this is in fact a GIST should be entertained.