Diagnosis

History

Presenting Complaint

Patients may present with abdominal pain, bloating, or gastrointestinal haemorrhage (haematemesis, melaena). Incidental finding of GIST is uncommon but accounts for a significant number of diagnoses.

Family History

Germline mutation of the KIT gene is similar to germline mutation of APC for familial adenomatous polyposis; patients with this condition may develop widespread GISTs of the small bowel and stomach.

Examination

A large abdominal mass may be palpable. Liver metastases are more common with GIST than for other sarcomas and the liver may be enlarged.

Imaging

CT remains the 'gold standard' investigation, as it provides good detail for masses associated with the mobile parts of the gastrointestinal tract. It also provides adequate imaging of the liver and regional nodes. MRI may have a role when GIST arises in places where MRI is conventionally used for carcinomas (eg. rectum). The typical appearance of GIST is of a smooth, uniformly enhancing mass; larger tumours (> 10 cm) may be heterogenous due to internal haemorrhage or necrosis. Liver metastases are suggestive of GIST; lung metastases of leiomyosarcoma.

Histological Diagnosis

Similar to mesenchymal tumours at other sites, pre-operative biopsy has the potential to cause tumour spillage or seeding of the biopsy tract. For this reason, biopsy under endoscopic ultrasound is preferred if there is any doubt as to the nature of the lesion. In patients with a high likelihood of GIST (appropriate age, imaging features), with localised disease, or who do not require neoadjuvant therapy, pre-operative biopsy may be avoided.

Staging

The main features which increase the rate of poor outcomes for GIST include:

  • Metastatic disease
  • Size of the primary lesion
  • Mitotic activity
  • Location

Lesions under 5 cm are rarely aggressive but have a poor outcome if they have a high mitotic rate. Larger lesions frequently have a high mitotic rate. Tumours arising in the stomach (20% mortality) have a better outcome than those from other sites (40%) and staging is split along these lines.

T Stage

  • T1: < 2 cm
  • T2: 2-5 cm
  • T3: 5-10 cm
  • T4: > 10 cm

N stage

  • N1: Regional nodal metastases (rare)

M Stage

  • M1: Distant metastases (usually to liver)

Mitotic Rate

  • Low: < 5 mitoses per 50 high power fields (grade 1)
  • High: > 5 mitoses per 50 high power fields (grade 2)

Final Stage (Stomach)

Stage T N M Mitotic Rate Likelihood of Progression
IA T1-2 N0 M0 Low 1%
IB T3 N0 M0 Low 4%
II T1-2
T4,,		 N0 M0 High
Low		 15%
IIIA T3 N0 M0 High 50%
IIIB T4 N0 M0 High 85%
IV TAny N1
NAny		 M0
M1		 Any 100%

Final Stage (Other GI Sites)

Stage T N M Mitotic Rate Likelihood of Progression
I T1-2 N0 M0 Low 1%
II T3 N0 M0 Low 25%
IIIA T1
T4		 N0 M0 High
Low		 50%
IIIB T2-4 N0 M0 High 80%
IV TAny N1
NAny		 M0
M1		 Any 100%

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