a) Leukaemia of T-Cells

There are a number of T-cell leukaemias which are all uncommon when compared to the B-cell types.

T-Cell Prolymphocytic Leukaemia

Accounts for 2% of mature, adult lymphocytic leukaemias. The median age of diagnosis is 65. About 20% of patients will have skin involvement; most have hepatosplenomegaly and lympho node involvement. Importantly, HTLV-1 is negative.
The cells are larger than typical lymphocytes. CD2, CD3 and CD7 are positive. The characteristic genetic abnormality is an inversion translocation of chromosome 14 - t(14,14). This leads to a linking of the TRA@ gene locus to either TCL1A or TCL1B, which both function as oncogenes.
T-Cell prolymphocytic leukaemia is an aggressive disease and survival is usually under a year.

T-Cell Large Granular Lymphocytic Leukaemia

Another rare mature leukaemia of adults, accounting for about 2% of these diagnoses. It occurs in similar age groups to T-Cell prolymphocytic leukaemia but follows an indolent course. On microscopy the cells contain a significant amount of granular cytoplasm. The cells bear some genetic resemblance to cytotoxic T lymphocytes. There are no specific genetic features. Median survival is 13 years.

Adult T-Cell Leukaemia/Lymphoma

ATLL is a disease of adults and almost always arises in patients infected with endemic Human T-Cell Leukaemia Virus Type 1 (HTLV-1). About 2.5% of patients infected with HTLV-1 develop ATLL; most of these patients originate from southern Japan, the Carribean and central Africa.
Most patients present with a combined leukaemia and lymphoma. Extranodal involvement is commmon, particularly skin. On blood smears, there are large lymphocytes with irregular nuclei. Most cells stain for CD4 and not CD8 but this is not a consistent rule; staining is usually positive for CD2, CD3 and CD5.
If lymphoma is present then survival is very limited, sometimes less than two weeks.