Introduction

• See also leukemia Leukemia.
• Definition: malignant neoplasm of unknown etiology consisting of immature, poorly differentiated lymphoblasts originating primarily in the bone marrow, with possible secondary infiltration of lymphatic organs. Neoplastic cells may or may not be circulating in the peripheral blood and can occasionally originate in the spleen.
• Signs: non-specific but often severe:
  • Weakness.
  • Anorexia
  • Vomiting.
  • Diarrhea.
  • Pyrexia.
• Clinial findings:
  • Profound cytopenias: neutropenia, thromboctopenia, anemia.
  • Leukocytosis with massive numbers of lymphoblasts.
  • Infiltration of blast cells into spleen, liver, lymph nodes, other sites.
• Diagnosis: blast cells in bone marrow, usually with similar cells in peripheral circulation; differentiate from other leukemias by cytochemical/ immunohistochemical staining (including flow cytometry) or PCR for antigen receptor rearrangement (PARR), and from lymphosarcoma by much milder lymphadenopathy, large numbers of circulating lymphoblasts, more severe myelosuppression, positive staining to CD34 (surface glycoprotein expressed on immature hematopoietic progenitor cells but not on more mature/ differentiated cells) upon flow cytometry.
• Treatment: supportive and cytotoxic agents may be tried.
• Prognosis: poor due to severe bone marrow infiltration and pancytopenia.

Pathogenesis

Etiology

• Unknown; ? effect of oncogenic retroviruses, ionizing radiation, chemical exposure.

Pathophysiology

• Neoplastic transformation → proliferation of early lymphoid cells → arrest of normal cell lineage differentiation → myelophthisis in bone marrow → profound cytopenias.
• Lymphoblasts present in peripheral circulation → infiltration of spleen and liver → organomegaly → possible infiltration of lymph nodes → lymphadenopathy; may also see infiltration of nervous system and gastrointestinal tract.
• Thrombocytopenia → petechiae, ecchymoses.

Timecourse

• Weeks.

Diagnosis

Treatment

Outcomes