We have diagnosed LGL-leukaemia in 52 patients over a 6-year period. If LGL- leukaemia only comprises 2 – 5 % of all T/NK-lymphoproliferative diseases, as indicated by the literature (8), this is a surprisingly high number. We believe that the disease is probably underdiagnosed. The prognosis is good (median survival 14.5 years) if the cytopenia is treated (also in patients who have serious granulocytopenia ), and survival is probably similar to that in an age-adjusted control group. This implies that the disease prevalence has a certain magnitude.
In our material there were similar numbers of men and women and the median age at diagnosis was 59 years. The clinical symptoms in our patients were almost exclusively related to cytopenias, and neutropenia with repeated infections was the most common clinical phenotype. In our patients, we also found a high prevalence of other diseases with immunopathogenesis. Our material corresponds well with the literature in this respect (6) – (9).
MGUS was identified in eight patients, i.e. 44 % of patients for whom the result of protein electrophoresis was known to us and 15 % of the entire material. The prevalence of MGUS in an unselected Caucasian population with the same median age is about 3 % (10). Viny and collaborators have recently reported a corresponding high prevalence of clonal B-cell disease in LGL-leukaemia (11).
Cytopenias in adult patients without a clear cause, should raise suspicion of LGL-leukaemia (11). Some have questioned the legitimacy of this diagnosis; in our opinion it is useful even if we agree that the term leukaemia may be challenging when informing patients. Firstly, the diagnosis can be the end of long-winded diagnostic efforts. Secondly, the diagnosis may lead to effective treatment when indicated.
Drug treatment, in the form of cyclosporine or methotrexate, is not cytoreductive but immunomodulating. However, one may see a reduction of the number of tumour cells in blood and bone marrow with methotrexate treatment, but this is not regarded as essential for the treatment effect. We do not have exhaustive information about treatment results in this patient material, but treatment results for eight of the patients have been published earlier as part of a larger international multicentre study (9). Cyclosporine and methotrexate are regarded as equal treatment alternatives, and response is expected in 80 % of the patients (9). In a small minority of patients it may be indicated to combine the immunomodulating treatment with G-CSF or erythropoietin. The effect is usually sustained with persistent immunomodulating treatment, even if the cytokine treatment is discontinued (9). The immunomodulating treatment can usually not be discontinued without loss of effect even if the remission may persist for years after end of treatment in a few patients (9). Powerful cytoreductive treatment will often prove to be ineffective (12). No published results are available that recommend treatment in those rare patients where LGL-leukaemia have an aggressive phenotype. The presentation in one of our patients had much in common with T-PLL, and we therefore chose a treatment strategy as for this condition (13).
At least a third of patients were asymptomatic, and especially in these one may naturally ask whether it was right to diagnose them with LGL-leukaemia. It is possible that the term MTL (monoclonal T-lymphocytosis), which so far has not been launched internationally, would be at least as suitable, and at least as easy to relate to for the patients. MBL (monoclonal B-lymphocytosis) has been launched as a term in cases where there is a clonal expansion of mature B-lymphocytes, but only in cases where the diagnostic demands for chronic lymphatic leukaemia or other chronic lymphoprolipherative disease have not been met (14). LGL-leukaemia of the indolent type seldom or never shows any substantial progression as a tumour disease, and transformation to an aggressive prolipherative disease is rare (15). Therefore, there are arguments for using the MTL term instead of T-LGL- leukaemia, especially in cases where patients lack clinical manifestations.