University of Virginia Health System

Prolymphocytic T Cell Leukemia
(T Cell PLL) 

 
Prolymphocytic T cell leukemia (T cell PLL)- Peripheral blood smear, Wright-Giemsa stain, 1000x

Description:

The morphologic features of T-PLL are indistinguishable from B-PLL by light microscopy, except for a tendency for more convolution of the nucleus in T-PLL. The cell size is 1½-2 times that of B-CLL cells, the cytoplasm is more abundant and is basophilic (blue) in color. Cytoplasmic membrane blebs are common. The nucleus varies in shape: round, clefted, convoluted. The nuclear chromatin is immature with clumping, and prominent nucleoli are frequently visible.

A small cell variant is recognized and represents approximately 20% of cases. As the name implies the cells are smaller with more condensed nuclear chromatin, and nucleoli usually are not as visible.

Immunophenotype:

The clonal cells are CD3+, CD4+, CD5+, and CD7+ in a majority of cases. Some express both CD4 and CD8 (double positive). Final proof of clonality may require molecular genetic studies.

Cytogenetics:

No signature cytogenetic abnormality has been identified. 8q trisomy and inversion of chromosome 14 are seen in up to 80% of cases.

Clinical and Laboratory Manifestations:

Like B-PLL the typical case presents with splenomegaly and a marked lymphocytosis (≥100,000mm³), but unlike B-PLL, lymphadenopathy is common, and shin involvement occurs in approximately 20%.

Differential Diagnosis:

• Sezary syndrome- mycosis fungoides:
• Once T cell lineage is established, Sezary syndrome is in the differential. The clonal cells in the peripheral blood in Sezary syndrome may be small or large or a mixture; and the cytoplasm is less resulting in a higher nuclear:cytoplasmic ratio, and is less basophilic. The nuclear chromatin tends to be much more convoluted, a characteristic though not diagnostic feature in Sezary syndrome and mycosis fungoides.
• The skin involvement in Sezary syndrome is a defining feature and very distinctive (generalized erythrodermia) whereas in T cell PLL shin involvement is mostly spotty, and occurs in only about 20% of cases.
• The immunophenotype in Sezary syndrome and mycosis fingoides (CD3+, CD4+, CD8-, CD2+, CD5+, and usually CD7-) is distinctively different from that in T-PLL which is CD3+, CD2+, CD5+, CD7+, and most express of CD4. Some, however, are CD8+, some are CD4+ and CD8+ (double positive), and some CD4- and CD8- (double negative).
• Adult T cell leukemia/lymphoma:
• The marked variation in the nuclear size and shape together with a positive serology for HTLV-1 retrovirus in adult T cell leukemia-lymphoma separates the two disorders. The presence of hypercalcemia and the aggressive course in adult T cell leukemia/lymphoma are also distinctive features.
• T cell subset of large granular lymphocyte syndrome:
• The morphologic appearance of the large granular lymphocytes on a Wright-Giemsa stain of a peripheral blood smear is diagnostic. Colabeling with CD8 and CD57 is also a characteristic feature.
• Hepatosplenic γδ T cell lymphoma/leukemia:
• The morphology of the cells are similar to those with T-PLL except that the cytoplasm is less and is clear to grey in color. The age difference at presentation is very different; most cases of hepatosplenic γδ T cell lymphoma/leukemia occur in children and young adults, and the immunophenotype is also characteristic: CD3+, double negative (CD4- and CD8-), CD5-, and, most importantly, express the γδ TCR instead of the αβ TCR.

Prognosis:

Poor. Like B-PLL the course usually is aggressive and response to most chemotherapy regimens is minimal. Also similar to B-PLL response to humanized anti-CD52 monoclonal antibody (alemtuzumab, Campath-1H has been encouraging).

General References:

• Jaffe ES, Harris NL, Stein H, Vardiman JW, eds. Pathology and genetics of tumours of hematopoietic and lymphoid tissues. Vol. 3 of World Health Organization classification of tumors, Lyon, France: IARC Press, 2001  
• Keren DF, McCoyd JP, Carey JL (eds). Flow cytometry in clinical diagnosis, 3rd ed. Chicago, ASCP Press, 2001
• Matutes E, Brito-Babapullo V, Swansbury J, et al. Clinical and laboratory features of 78 cases of T prolymphocytic leukemia. Blood 78: 3269, 1991

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