Table 1 outlines the diagnostic criteria for T-PLL. A diagnosis of T-PLL requires the demonstration of the first three major diagnostic criteria. The initial two major criteria are considered defining characteristics of the disease. While the third major criterion, involving alterations in TCL1a or MTCP1, is prevalent in most T-PLL cases, it is not universally present [4]. This evidence concerns the gene MTCP1 and T-cell prolymphocytic leukemia.