Cluster 1331: wbc white blood cell count mm mcl days hydroxyurea registration Cluster 1582: white cells wbc blood mcl days ml ul wbcs administration Cluster 1737: white blood count cell mm ul hydroxyurea cells mcl meet Cluster 2090: mcl platelet count cells thrombocytosis pi days transfused marrow mm Cluster 2292: blast count hydroxyurea peripheral circulating blood marrow counts ul mm