High abundance of circulating megakaryocytic cells in chronic myeloid leukemia in Indian patients. Revisiting George Minot to re-interpret megakaryocytic maturation.

Circulating megakaryocytic cells abound in chronic myeloid leukemia (CML) seen in India and uniquely provide a setting for observing megakaryocytic maturation in the peripheral blood, a milieu not native to megakaryocytes. Peripheral blood megakaryocytic cells were studied in 324 cases of CML (235 chronic, 65 accelerated and 24 blastic phases). Two maturation themes were evident. Megakaryocytic blasts, especially in some cases of blast crisis, precociously make a foray into platelet formation and end up producing huge agranular or poorly granular cytoplasmic lobulated masses, that break off and come to lie in the circulation. This evidence of unsuccessful effort may exist, in a considerably attenuated form in chronic phase, alongside of the second major theme of megakaryocytic maturation centered around the familiar micromegakaryocyte, characteristic of the chronic phase. This cell is regarded as dysplastic, but produces morphologically normal platelets. The possibility that this occurs via a hitherto unstudied alternative path of platelet maturation that plays out in the peripheral blood, and the contrasting disorderly premature attempt of blasts to form platelets, represent exciting maturation processes that need further study. Our observations fortuitously constitute a revisit of the insightful exposition on the subject by George Minot nearly a century ago.