Precursor B Lymphoblastic Lymphoma

Definition

Lymphoma with morphologic and immunologic features of precursor B cells; at presentation the primary site of involvement must not be bone marrow or peripheral blood

Morphologically indistinguishable from B Lymphoblastic Leukemia
- Presence of a mass lesion and <25% blasts in marrow required for diagnosis of lymphoma
  - Criteria for separation are arbitrary
- >80% of precursor B neoplasms are leukemic
- Precursor B leukemia and lymphoma are considered manifestations of the same disease
Diffuse effacement of node architecture
- No true nodular pattern
  - May be pseudonodular with fine fibrous bands
- Rare partial node involvement
  - Paracortical and parafollicular
- Frequent soft tissue involvement
- Fragile cells may show crush or smear artifact
Small to medium sized cells in most cases
- Atypical or large cell variant
  - Reported in 10% of cases
  - Slightly larger nuclei
  - May contain nucleoli
  - No clinical significance
Round to oval nuclei with fine chromatin
- Thin nuclear membrane
- Nucleoli few and inconspicuous
- Convoluted nuclear membranes in most cases
- Frequent mitotic figures
Scant cytoplasm
- Imprints show rare vacuoles and coarse PAS+ granules
Immature B phenotype

Yasodha Natkunam MD PhD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342