Regression der Philadelphia-Chromosom (bcr/abl)-positiven Myelo- und Megakaryopoiese unter Imatinib(STI571)-Therapie bei chronischer myeloischer Leuk�mie (CML)

Langerhans Cell Sarcoma in a Chronic Myelogenous Leukemia Patient Undergoing Imatinib Mesylate Therapy

Langerhans cell sarcoma (LCS) is a rare malignancy requiring differential diagnosis from other high-grade nonhematologic and hematologic tumors. The pathogenesis of LCS remains unknown. Notably, LCS and its benign counterpart, Langerhans cell histiocytosis (LCH), are frequently associated with other malignancies. To the best of our knowledge, we describe the first case of LCS in a chronic myelogenous leukemia (CML) patient undergoing imatinib mesylate therapy. We performed molecular cytogenetic analyses for investigating the association between LCS and CML. In our case, molecular cytogenetic analysis did not reveal BCR-ABL1 fusion and BRAF V600E mutation, suggesting that LCS may be coincident in this patient. However, recurrent BRAF V600E mutation has been found in LCH. Published reports have revealed the clonal relationship between LCH/LCS and other hematologic malignancies, especially lymphoid neoplasms. However, there are only 2 reports demonstrating the clonal relationship between LCH and myeloid neoplasms. The association of LCH/LCS with myeloid neoplasms and the role of BRAF V600E mutation in LCS are discussed.

[Hematological side effects of tyrosine kinase inhibition using imatinib]

Imatinib (STI571, Gleevec/Glivec) and other small-molecule tyrosine kinase inhibitors are highly effective in the treatment of chronic myeloid leukemia (CML), gastrointestinal stromal tumors and, for example, eosinophilia-associated chronic myeloproliferative disorders. This molecularly targeted approach disrupts abnormal tyrosine kinase dependent signalling pathways, thus providing a preferred treatment option for selected neoplastic disorders with activating mutations of Abelson-, Abl-related-, Kit-, and platelet-derived growth factor receptor A and B genes. Loss of response to imatinib may be due to an acquired resistance of emerging mutant tumor cell clones. Therapy is generally well tolerated. However, toxicities including edema, skin rashes, fatigue, nausea and myelosuppression have been reported. Philadelphia/Bcr-Abl-negative clonal chromosomal abnormalities may develop. Bone marrow trephines obtained from CML patients in complete remission with prolonged pancytopenia secondary to imatinib generally show marrow hypoplasia. Morphological features may be in keeping with either aplastic anemia or myelodysplasia developing in Philadelphia-negative hematopoiesis. Single or multilineage myelodysplasia may be accompanied by an excess of blasts and rarely evolves into acute leukemia in CML patients. Severe adverse hematological effects of imatinib are extremely rare. Current questions involve the molecular mechanisms of hematological side effects of tyrosine kinase inhibitors with special regard to the emergence of distinct aberrant clones.