Pathologic complete response to neoadjuvant imatinib of a gastric stromal tumor with concomitant mutations in KIT: A case report and literature review

Abstract

Key clinical message: We report the first case of pathologic complete response (pCR) to neoadjuvant imatinib in a gastric stromal tumor harboring KIT mutations in both exons 11 and 9. The significance of this co-occurrence is unknown and might increase the responsiveness of gastrointestinal stromal tumors (GISTs) to imatinib.

Abstract: pCR of GIST to neoadjuvant imatinib is rare. We report a case of pCR to neoadjuvant imatinib in a gastric stromal tumor that harbored co-occurrence of multiple KIT mutations in exons 11 and 9. This co-occurrence in exons 9 and 11 is the first to be reported in the English literature.

Keywords: KIT; PDGFRA; imatinib; mutation; pathologic complete response.

FIGURE 1

Abdominal CT scan injected at portal time showing a rounded mass with circumscribed contours and heterogeneous enhancement with central necrotic areas. The enhancement is moderate after injection of contrast. It is mainly exophytic at the expense of the small curvature of the stomach close to the body of the pancreas and the first jejunal intestines with loss of the fatty safety border.

FIGURE 2

(A) Dense spindle cell proliferation (HE ×200). (B) Strong expression for c‐KIT (IHC ×200).

FIGURE 3

The structure of KIT protein. Panel (A) is a representation of the protein surface. On the left, the 1T46 structure and on the right the mutated KIT protein model. Panel (B) is a cartoon representation of the 1T46 (on the left) and the mutated KIT model (on the right) with a zoom on the mutated residues shown in green carbon licorice representation. The STI‐571 molecule is shown in pink carbon licorice on all sub‐figures.

FIGURE 4

The postoperative CT scan at portal time shows 50% regression of the mass syndrome with only minimal fat infiltration remaining.