Gastrointestinal Stromal Tumour

Introduction

Gastro-intestinal stromal tumours (GISTS) are a rare form of gastrointestinal neoplasm, however they are the most common mesenchymal tumour of the gastrointestinal tract.  Approximately 700 new cases are diagnosed each year in the UK.  Diagnosis is mainly by clinical features and standard histopathology including immunostaining.

A majority of GISTs have been found to have activating mutations in one of two tyrosine kinase genes KIT and PDGFRA.  The majority ~65% have acquired activating mutations in KIT whereas ~3% have acquired activating mutations in PDGFRA.

Imatinib is useful in the clinical management of patients with GIST, with the majority of GISTs showing a good response to imatinib therapy.  Imatinib is only approved for use in GIST where the diagnosis has been confirmed either by KIT immunostaining or positive mutation analysis.

Referral information

Formalin fixed paraffin embedded (FFPE) tissue is preferred. We recommend 10 x 10µM thick unstained, unmounted sections sealed in a clean 1.5mL Eppendorf tube. The tissue sample should have been reviewed by a histopathologist to determine suitability for testing and estimate tumour cell content. A 20% or greater ratio of tumour to normal tissue in the submitted sample is required for optimum mutation detection. Other samples may be acceptable and macrodissection can be considered for samples with low tumour cell content, however, please contact the laboratory for guidance first.

Price & reporting times

Test Price (NHS) Price (non-NHS) TRT
GIST mutation screen POA POA  28 days

Test validation & quality assurance - information for users

The test has been validated on DNA samples with KIT and PDGFRA mutations.  Mutations within the tested exons can be detected down to a level of at least 20% in the sample submitted for testing. Each sample is assayed in duplicate to ensure consistency. Fewer than 10% of GISTs are mutation negative after screening. Negative results should be correlated with histopathological and clinical information.

Sample requirements

5 x 5µM FFPE unstained slide mounted sections (without coverslips) from a tissue block selected to have maximum neoplastic cell content. If neoplastic cell content is less than 30% and the sample is suitable for macrodissection, please send an accompanying H&E stained guide slide prepared from a neighbouring section with the region of neoplasia clearly marked out. Where neoplastic cell content is greater than 30%, 5 x 5 µM FFPE sections as unmounted scrolls in a clean, unused, tube or container manufactured under aseptic conditions is acceptable.

Referral guidelines

Please see our referral guidelines for more information.

OMIM Number(s) - 164920, 173490

Gene(s) - KIT, PDGFRA

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