Clonal Replacement Underlies Spontaneous Remission in Paroxysmal Nocturnal Haemoglobinuria.
Paroxysmal nocturnal haemoglobinuria (PNH) terminating in acute leukaemia (AL) is an infrequent condition. In several cases, flow cytometric analysis of glycosylphosphatidylinositol anchored membrane proteins such as DAF and CD59/MACIF has suggested the leukaemic cells to be derived from the PNH clone, thereby implicating PNH as a potential preleukaemic disease. In the present paper, we review the data for one patient treated in our hospital and 20 cases reported in the literature from 1969 to 1993. The sex ratio is 1 female/2 males, mean age at diagnosis of PNH was 46 years and the mean interval between the diagnoses of PNH and AL was 53 months. AL type was AML M6 in 8 patients, other types of AML in 12 and ALL in one, with a mean survival of 7.1 months following diagnosis of AL. In all cases analyzed, the PNH phenotype of erythrocytes disappeared with progression of AL, whereas reappearance of this phenotype with complete remission of AL was inconstant. PNH would thus appear to be a potential preleukemic disease. When this disorder terminates in AL, the type is often AML M6, although ALL is also possible. The prognosis of AL in PNH is poor as for other secondary leukaemias. Apart from marrow aplasia, leukaemic transformation is another life threatening complication of PNH which may justify allogeneic bone marrow transplantation (allo-BMT) and potential leukaemic transformation can therefore be an additional argument in favour of allo-BMT when pancytopenia develops in PNH patients.