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  • T-cell large granular lymphocytic leukemia (T-LGLL) results from an indolent clonal expansion of large granular lymphocytes (LGLs) with a T-cell (CD3+) phenotype and a clonal T-cell receptor gene rearrangement(s), usually α and β chains.

  • Diagnosis of T-LGLL requires an arbitrary level in the blood of CD3+CD8+CD57+ cells that is greater than 0.5 × 109/L maintained for at least 6 months. CD5 is dimly expressed.

  • Chronic lymphoproliferative disorders of natural killer cells (CLPD-NK) is a clonal expansion of LGL with a NK cell (CD3–) phenotype. It lacks convenient markers to determine clonality, such as antigen receptor rearrangements. (See Chap. 67.)

  • Diagnosis of CLPD-NK requires an arbitrary level in the blood of CD3–CD8+CD16+ and/or CD16+CD56+ cells that is greater than 0.75 × 109/L maintained for at least 6 months.


Etiology and Pathogenesis

  • In T-LGLL, it is postulated, based on complementarity determining region 3 (CDR3) patterns and Vβ family usage, that this malignancy arises secondary to chronic antigen stimulation.

  • Most patients are not infected with either HTLV-I or HTLV-II.

  • Cytomegalovirus is possibly implicated in rare cases of CD4+ T-LGLL.

  • Chronic immune dysregulation and aberrant cytokine production may contribute to the LGLL proliferation and survival.

  • Platelet-derived growth factor (PDGF) and interleukin (IL)-15 appear to be the key cytokines regulating LGLL proliferation and survival.

  • Constitutive overexpression of Fas (CD95) and the Fas ligand (CD178), which also is found at high levels in patients’ sera, may also contribute to the LGL proliferation.

  • Chronic activation of the JAK/STAT3 pathway is a hallmark of LGLLs.

  • Gain-of-function STAT3 mutations have been demonstrated in 28% to 75% of cases of T-LGLL and 30% to 48% of cases of CLPD-NK. STAT5B mutations are also found but less frequently.

Clinical Features

  • About half the patients with T-LGLL are asymptomatic at diagnosis, and diagnosis is based on examination of blood (Table 58–1).

  • About half of patients have palpable splenomegaly.

  • About one-third of patients have recurrent bacterial infections.

  • “B symptoms” (eg, low-grade fevers, night sweats, and/or weight loss) (aggressive variant) are very infrequent.

  • About one-fourth of patients have rheumatoid arthritis, often with features of Felty syndrome.

  • Less than one-tenth of patients have lymphadenopathy.


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