T Prolymphocytic Leukaemia

Morphological features

• Usually marked lymphocytosis.
• Atypical lymphoid cells with clumped chromatin
• Single, indistinct nucleolus – may be more apparent at lower magnification.
• Cytoplasmic blebbing is common.
• Minimal basophilic, agranular, cytoplasm.
• Morphological variants (not associated with distinct clinical presentation or outcomes):
  • Small cell (20%), nucleoli invisible by light microscopy.
  • Sezary (5%) with irregular, cerebriform nuclei.

Distinguishing T-PLL from B-PLL

Feature	B-PLL	T-PLL
Cytoplasm	Large amounts	Minimal
Blebbing	None	Cytoplasmic projections in some cells
Nucleoli	Prominent	Subtle and indistinct
Size	Large	Small to medium-sized
Nuclear outline	Regular	Irregular
Immunophenotype	CD20+/19+/SmIg++/22+ CD79a+/23-/5variable	CD3+/2+/5+/7++/1a-/TdT- Typically TCL1+ (>90%) and CD52+ Usually 4+/8- (60%), or 4+/8+ (25%) Characterised by lack of phenotypic aberrancy
Cytogenetics	13q deletion 11q deletion 17p deletion 6q deletion	t(14;14) Inversion 14 Iso8q, trisomy 8, occasionally complex

Diagnostic Criteria

Requires all three major criteria or two major + one minor criteria.

• Major criteria
  • >5 × 10⁹/L cells of T-PLL phenotype in peripheral blood or bone marrow 
  • T-cell clonality (by PCR for TCR-ß/TCR-Γ, or by flow cytometry) 
  • Abnormalities of 14q32 or Xq28 OR expression of TCL1A/B, or MTCP1
• Minor criteria
  • Abnormalities involving chromosome 11 (11q22.3; ATM) 
  • Abnormalities in chromosome 8: idic(8)(p11), t(8;8), trisomy 8q 
  • Abnormalities in chromosome 5, 12, 13, 22, or complex karyotype 
  • Involvement of T-PLL specific site (eg, splenomegaly, effusions)