T-cell prolymphocytic leukemia

T-cell-prolymphocytic leukemia (T-PLL) is a mature T-cell leukemia with aggressive behavior and predilection for blood, bone marrow, lymph nodes, liver, spleen, and skin involvement.^[1] T-PLL is a rare leukemia, primarily affecting adults over the age of 30. It represents 2% of all small lymphocytic leukemias in adults.^[2] Other names include: T-cell chronic lymphocytic leukemia, "Knobby" type of T-cell leukemia, T-prolymphocytic leukemia/T-cell lymphocytic leukemia^[1]

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Clinical Features

Due to the systemic nature of this disease, leukemic cells can be found in peripheral blood, lymph nodes, bone marrow, spleen, liver, skin.^[1]

Etiology

It is postulated that the originating cell line for this disease is a mature (post-thymic) T-cell.^[1]

Clinical Presentation

Patients typically have systemic disease at presentation, including hepatosplenomegaly, generalized lymphadenopathy, and skin infiltrates.^[1]

Laboratory Findings

A high lymphocyte count (> 100 x 10⁹/L)along with anemia and thrombocytopenia are common findings. HTLV-1 serologies are negative, and serum immunoglobins are within normal limits with no paraproteins present.^[1]

Morphology

In the peripheral blood, T-PLL consists of medium-sized lymphocytes with single nucleoli and basophilic cytoplasm with occasional blebs or projections. The nuclei are usually round to oval in shape, with occasional patients having cells with a more irregular nuclear outline that is similar to the cerebriform nuclear shape seen in Sézary syndrome.^[3] A small cell variant comprises 20% of all T-PLL cases, and the Sézary cell-like (cerebriform) variant is seen in 5% of cases.^[3]

Marrow involvement is typically diffuse with morphology similar to what is observed in peripheral blood.^[1] In the spleen, the leukemic cell infiltrate both the red pulp and white pulp, and lymph node involvement is typically diffuse through the paracortex.^[1]. Skin infiltrates are seen in 20% of patients, and the infiltrates are usually dense and confined to the dermis and around the skin appendages.^[2]

Molecular Findings

Immunophenotype

T-PLL has the immunophenotype of a mature (post-thymic) T-lymphocyte, and the neoplastic cells are typically positive for pan-T antigens CD2, CD3, and CD7 and negative for TdT and CD1a. The immunophenotype CD4+/CD8- is present in 60% of cases, the CD4+/CD8+ immunophenotype is present in 25%, and the CD4-/CD8+ immunophenotype is present in 15% of cases.^[2]

Genetic Findings

Clonal TCR gene rearrangements for the γ and δ chains are typically found. The most frequent chromosomal abnormality is the inversion of chromosome 14, specifcally inv 14(q11;q32). This is found in 80% of cases, while 10% of cases show a reciprocal translocation of chromosome 14 (t(14;14)(q11;q32)). ^[4]

^[5] Also, abnormalities of chromosome 8 are seen approximately 75% of patients, including idic (8p11), t(8;8)(p11-12;q12), and trisomy 8. ^[6]

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