Chronic Myeloid Leukemia in Two Patients with Gastrointestinal Stromal Tumor.

Imatinib competitively binds to the ATP binding site of Bcr-Abl kinase and inhibits Abl tyrosine kinase activity. Most patients with chronic myeloid leukemia (CML) achieve clinically relevant hematologic and cytogenetic responses to imatinib. It is also a potent inhibitor of a receptor-type c-Kit tyrosine kinase. Therefore, it was examined for therapeutic efficacy against malignant Gastrointestinal Stromal Tumor (GIST), which is a rare tumor of the gastrointestinal tract and is mainly caused by aberrant expression of a mutated c-Kit that is constitutively active without binding of a ligand, stem cell factor. We report two rare cases of double cancer involving CML and GIST. The first case is a 66-year-old Japanese male patient who was presented to our hospital with leukothrombocytosis on February 27, 2006. The patient was diagnosed to be suffering from CML by the presence of Philadelphia chromosome. Several days later, he was admitted with acute peritonitis. A ruptured tumor on 80 cm oral side of ileum end was found by an emergency partial ilectomy. Microscopically, spindle-shaped and round epithelioid cells were growing externally from the intestinal muscular propia. Immunohistochemical analysis showed that the tumor cells were positive for c-kit and CD34 and negative for S-100 protein and desmin. The tumors were identified as GIST. Imatinib was administered to treat CML on the 8th postoperative day. The second case is a 57-year-old Japanese female patient who was presented to our hospital with marked thrombocytosis on March 6, 2006. The patient was diagnosed to be suffering from CML by the presence of Philadelphia chromosome. One year ago, she underwent distal gastrectomy for submucosal tumor. Pathological examination revealed proliferation of submucosal spindle-shaped cells with elongated cigar-shaped nuclei arranged in fascicles. Immunohistochemical stains confirmed the diagnosis of GIST.

These two cases provided a valuable opportunity for treating GIST with CML. We look forward to active effect of imatinib, not only in CML treatment but also in preventing recurrence of GIST. The occurrence mechanism of either CML or GIST at the biomolecular level has been established. However, we can show no relation between these malignancies. Therefore, it is natural for us to understand accidental coincidence. We should follow-up these patients carefully. Accumulation of such cases may contribute to clarify more precise mechanism of tumorgenesis.