Fibrosis of the marrow is not cast in cement

We receive, from time to time, tantalizing bits of information and misinformation concerning fibrous conversion of the marrow. Forty years ago, we believed that removal of the large spleens of myelofibrosis was a too-great risk.1At that time, we subscribed to Donhauser's dictum that the metaplastic spleen in myelofibrosis with myeloid metaplasia (MFM) was the only source of blood cells, having resumed its fetal hemopoietic function.2Now we know it isn't true. The hemopoietic tissue in MFM is neoplastic with neoplastic cell-lines in the marrow and in the spleen; the two organs become involved simultaneously. The spleen's metaplasia is not a reaction to the marrow's abdication; the marrow is often hypercellular before it becomes fibrotic.3The fibrous tissue is not a part of the abnormal neoplastic clone: marrow fibroblasts do not share the chromosomal abnormalities that are often present in the neoplastic hemopoietic cells of the myeloproliferative