The incidence of myelofibrosis in essential thrombocythemia, polycythemia vera and chronic idiopathic myelofibrosis: a retrospective evaluation of sequential bone marrow biopsies - Kreft,A.; Buesche,G.; Ghalibafian,M.; Buhr,T.; Fischer,T.; Kirkpatrick,C.J. (Acta Haematol, 2005)