Stromal abnormalities in neoplastic bone marrow diseases.
Bone marrow malignancies are clonal disorders resulting from neoplastic transformation of hematopoietic stem or progenitor cells. Similar to their normal counterparts, transformed blood-forming cells remain dependent on signals from the hematopoiesis-regulating stromal environment for survival and proliferation. There is increasing evidence that the microenvironment may also take a more active part in the disease process. A review of the literature on stromal abnormalities in the leukemias, the myelodysplastic syndromes, and multiple myeloma reveals three principal mechanisms by which stromal derangements can contribute to the evolution of a neoplastic disease. In the simplest case, neoplastic blood-forming cells induce reversible changes in stroma function or composition which result in improved growth conditions for the malignant cells ('malignancy-induced microenvironment'). In the second setting, functionally abnormal end cells derived from the malignant clone become an integral part of the stroma system, selectively stimulating the neoplastic cells and inhibiting normal blood cell formation ('malignant microenvironment'). In the third condition, the emergence of a neoplastic cell population is the consequence of a primary stroma lesion characterized by inability to control regular blood cell formation ('malignancy-inducing microenvironment'). The perception of different stroma-related disease mechanisms may eventually lead to the development of alternative therapeutic approaches.