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Radiologic Evaluation of Gastrointestinal Stromal Tumors ( GISTs)
View City Scan

This series of CT scans and PET scans illustrates some of the possible outcomes following treatment with a KIT inhibitor. Click on the descriptions below to view the images and brief commentary on the interpretation of the findings.


Partial
Responses
Stable
Disease
Limited
Progression
Generalized
Progression
Indeterminate Response

Decrease in tumor size1

This is an example of partial responses in multiple tumors. The identifying features on these CTs are decreases in tumor size.

Scan A

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Scan A shows metastatic GISTs in the liver, as noted by the white arrows. The large gray area comprising the right half of this scan is also a GIST, although it has not been highlighted with arrows.
Scan B

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Scan B was taken 3 months after treatment initiation and shows a clear decrease in the size of the tumors, signifying response to treatment. Even the unmarked tumor on the right side of the scan is smaller. Decrease in tumor size is just 1 of the features that may represent a response in GIST.
These images are from a single patient and may not be typical or representative of all patients receiving treatment.
 

No change in tumor size with decrease in
tumor density2

This example shows partial response in multiple tumors. The features identifying this as an example of partial response are the lack of significant change in tumor size with a decrease in density.

In order to optimize radiologic evaluation of GISTs, it is important not to misinterpret darkening tumors on a CT image without a change in tumor size as treatment resistance or disease progression. The darkening of tumors indicates hypoattenuation, which signifies a partial response.

Scan A

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Scan A is a CT image of a GIST patient showing hepatic metastases identified by the white arrows.
Scan B

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Scan B is taken 2 months after treatment initiation, showing lesions that are homogeneous, with a decrease in attenuation, but not a substantial decrease in size. The decrease in tumor density is seen as darkening of the lesions on the CT image. This image signifies partial response to treatment.
These images are from a single patient and may not be typical or representative of all patients receiving treatment.
 

Increase in tumor size with decrease in
tumor density3

These images are from a single patient and may not be typical or representative of all patients receiving treatment.

This is an example of partial response in GIST characterized by 2 identifying features: an increase in tumor size with a decrease in tumor density.

This example highlights how judging tumor response by lesion size alone may not be adequate for an accurate evaluation. In some situations, an increase in tumor size with a decrease in tumor density represents a response to treatment. As in the prior example, the decrease in tumor density is seen as darkening of the lesions on a CT image.

Scan A

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Scan A is a CT image of a GIST patient with small bowel metastases identified by the white arrows.
Scan B

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Scan B was taken 2 months after treatment initiation. It shows lesions that have increased in size but are homogeneous and hypoattenuating. This signifies a partial response to treatment.
Scan C

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Scan C was taken 4 months after treatment initiation and shows that the top lesion has significantly decreased in size. The bottom lesion has continued to increase in size but remains hypoattenuating. This lesion became smaller on follow-up CT scans, signifying continued response.
 

References

  1. Shankar S, Vansonnenberg E, Desai J, Di Piro PJ, Van Den Abbeele A, Demetri GD. Gastrointestinal stromal tumor: new nodule-within-a-mass pattern of recurrence after partial response to imatinib mesylate. Radiology. 2005;235(6):892-898.
  2. Hong X, Choi H, Loyer EM, Benjamin RS, Trent JC, Charnsangavej C. Gastrointestinal stromal tumor: role of CT in diagnosis and in response evaluations and surveillance after treatment with imatinib. Radiographics. 2006;26(2):481-495.
  3. Demetri GD, Benjamin R, Blanke CD, et al, for the NCCN GIST Task Force. NCCN Task Force report: Optimal management of patients with gastrointestinal stromal tumor (GIST) - expansion and update of NCCN Clinical Practice Guidelines. J Nat Comprehensive Can Net. 2004;2(suppl 1):S-1-S-26.
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