T-cell Large Granular Lymphocytic Leukemia (T-LGLL) is a rare, indolent proliferation of large lymphocytes with azurophilic granules. Morphologically, they are indistinguishable from normal reactive LGL cells, but in the case of leukaemia they are persistently present in abnormal amounts, without signs of infection. Abnormal means >20% of lymphocytes or more than for 6 months.