High-grade KIT-negative sarcoma of the small bowel in a patient with chronic myeloid leukemia receiving long-term tyrosine kinase inhibitors

Gastrointestinal Stromal Tumor With Chondrosarcomatous Dedifferentiation Following Imatinib Therapy

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the digestive tract, followed by schwannomas, lipomas, leiomyomas, and vascular tumors. They arise more often in the stomach, followed by the small bowel, esophagus, and rectum. Imatinib mesylate, a tyrosine kinase inhibitor with activity against ABL, BCR-ABL, platelet-derived growth factor receptor-alpha (PDGFRA), and c-KIT (CD117), constitutes the cornerstone of treatment for inoperable or metastatic GIST. Cases showing disease progression or resistance to imatinib mesylate may retain their morphology or present unusual morphologic and immunohistochemical characteristics.

We herein describe a case of a 67-year-old patient with a previous history of GIST of the stomach, with local recurrence, who was admitted with a workup of lung nodule on chest computed tomography as part of the routine follow-up. The nodule was resected which showed a malignant tumor composedof epithelioid cells, with an abrupt transition to chondrosarcoma. Epithelioid cells were immunostained for CD117, DOG1, and Vimentin, whereas chondrosarcomatous cells expressed only Vimentin. These findings were consistent with metachronous pulmonary metastasis of the previously diagnosed GIST with chondrosarcomatous dedifferentiation. No KIT or PDGFRA mutation was detected. A review of all accessible pertinent papers disclosed 26 similar cases with unusual morphological and immunohistochemical findings, either post-imatinib treatment or, less commonly, de novo, with heterogeneous differentiation.

Awareness of the histological and immunohistochemical changes in GISTs post imatinib therapy is essential to avoid a severe diagnostic pitfall.

Ph-negative isolated myeloid sarcoma with NPM1 gene mutation in adolescent with Ph-positive chronic myeloid leukemia in remission after treatment with allogeneic bone marrow transplantation and imatinib mesylate

Few patients in remission of Ph-positive chronic myelogenous leukemia (CML) develop Ph-negative MDS/AML, usually with clonal cytogenetic abnormalities. Isolated Ph-negative myeloid sarcoma (MS) is presented here as a form of such disorder, different from Ph-positive MS establishing CML relapse in blastic phase. We describe 11-year-old male who developed Ph-negative isolated MS with NPM1 mutation, remaining in complete molecular remission of Ph-positive chronic myeloid leukemia treated with allo-HSCT in first chronic phase and with imatinib and donor lymphocyte infusion in molecular relapse. The possible mechanisms of the tumor formation are reviewed with stress on importance of comprehensive molecular/cytogenetic evaluations.