Studies of the bone marrow in polycythemia vera and the evolution of myelofibrosis and second hematologic malignancies

Abstract

The PVSG study is unique in that it is prospective and composed of 432 patients randomized to three treatment arms. This study also provides the opportunity for serial studies of numerous sequential biopsies. Large numbers of cases with sequential biopsies covering the entire long course are essential to appreciate the full spectrum of tissue changes in this disease. The PVSG was initiated in 1967 and in mid-1985 approximately one third of the patients are alive and on protocol. For these reasons, the results must still be considered preliminary. Pretreatment biopsies from patients randomized in the PVSG have been analyzed for total cellularity, megakaryocyte concentration, and reticulin content. Considerable variation in these elements was found in these biopsies. Sequential posttreatment biopsies from these patients have also been studied and correlated with the clinical course of the disease. None of the morphologic parameters analyzed was shown to be of prognostic significance. Early in the course of PV the marrow reticulin content is almost always normal. The length of the developmental stage is unknown and the precise timing of the clinical onset may be difficult. Therefore, the 11% of patients that showed a significant increase in reticulin on initial evaluation may have had PV longer than was indicated clinically. If large numbers of sequential biopsies are studied, an increase in reticulin content can frequently be demonstrated during the active phase of the disease and before the onset of the spent phase. Currently 39 patients (9%) have developed the spent phase, or PPMM. PPMM occurred in about the same incidence in the patients treated with myelosuppressive therapy as by phlebotomy alone, the spent phase occurring in 16 patients treated by phlebotomy alone, 11 with chlorambucil, and 12 with 32P. The course of the reticulin fibrosis is slowly progressive. There is some evidence for regression in a few patients in the erythrocytotic phase, but sampling variation cannot be completely ruled out. At this time in the study, AL has developed in 37 patients (8.6%). The incidence of AL is quite low in the phlebotomy group (three cases). Presumably this represents the natural incidence in PV unmodified by therapeutic agents. The frequency is approximately equal and quite high in the chlorambucil and 32P groups. There are 19 cases in the chlorambucil-treated group and 15 in the 32P-treated group. The leukemias that developed in the PV patients occurred either de novo or following PPMM.(ABSTRACT TRUNCATED AT 400 WORDS)