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Chronic Lymphocytic Leukemia (CLL)

Chronic Lymphocytic Leukemia (CLL) is a chronic lymphoproliferative malignancy characterized by the accumulation of mature but functionally incompetent B lymphocytes in the blood, bone marrow, lymph nodes, and spleen. It is the most common leukemia in adults in Western countries.

Also called

Chronic Lymphoid Leukemia

ICD-10

C91.1

Specialty

Hematology

Onset

Chronic

Reviewed

August 2026

On This Page

Overview

Chronic Lymphocytic Leukemia (CLL) is a slow-growing malignancy resulting from the clonal proliferation of mature B lymphocytes. The abnormal lymphocytes accumulate because of defective apoptosis rather than rapid proliferation, leading to lymphocytosis, lymphadenopathy, splenomegaly, bone marrow infiltration, and immune dysfunction.

Many patients are diagnosed incidentally on routine blood tests, while others present with fatigue, recurrent infections, enlarged lymph nodes, or cytopenias. 

Etiology & Risk Factors

-Etiology

The exact cause is unknown. Chronic Lymphocytic Leukemia (CLL) develops from acquired genetic abnormalities in mature B lymphocytes leading to impaired apoptosis and clonal expansion.

-Risk Factors

  • Increasing age (usually >60 years)

  • Male sex

  • Family history of CLL

  • Caucasian ethnicity

  • Monoclonal B-cell lymphocytosis (MBL)

  • Certain genetic abnormalities (e.g., del17p, TP53 mutation)

Pathophysiology

Acquired genetic mutations in mature B lymphocytes → impaired apoptosis → accumulation of abnormal monoclonal B cells in blood, bone marrow, lymph nodes, spleen, and liver → bone marrow infiltration reduces normal hematopoiesis causing anemia and thrombocytopenia → immune dysfunction leads to hypogammaglobulinemia and recurrent infections → autoimmune complications such as autoimmune hemolytic anemia and immune thrombocytopenia may develop.

Clinical Presentation

Symptoms

  • Fatigue

  • Weakness

  • Weight loss

  • Fever

  • Night sweats

  • Recurrent infections

  • Easy bruising

  • Bleeding

  • Abdominal fullness

  • Early satiety

Signs

  • Generalized lymphadenopathy

  • Splenomegaly

  • Hepatomegaly

  • Pallor

  • Petechiae

  • Purpura

History Taking

-Ask about:

  • Fatigue
  • Fever
  • Night sweats
  • Weight loss
  • Recurrent infections
  • Enlarged lymph nodes
  • Easy bruising
  • Bleeding
  • Abdominal fullness
  • Previous autoimmune disease
  • Family history of Chronic Lymphocytic Leukemia (CLL)
  • Previous malignancy

Physical Examination

-General Examination

Look for:

  • Pallor

  • Fever

  • Weight loss

  • Petechiae

  • Ecchymoses

-Lymphatic Examination

Assess for:

  • Cervical lymphadenopathy

  • Axillary lymphadenopathy

  • Inguinal lymphadenopathy

-Abdominal Examination

Assess for:

  • Splenomegaly

  • Hepatomegaly

Investigations

-Complete Blood Count (CBC)

Typical findings:

  • Persistent absolute lymphocytosis (≥5 × 10⁹/L)

  • Mild anemia

  • Thrombocytopenia (advanced disease)

-Peripheral Blood Film

Characteristic findings:

  • Small mature lymphocytes

  • Smudge (basket) cells

 

-Flow Cytometry (Diagnostic Test)

Confirms the diagnosis by demonstrating a characteristic immunophenotype:

  • CD5 positive

  • CD19 positive

  • CD20 (dim)

  • CD23 positive

  • Weak surface immunoglobulin

-Bone Marrow Aspiration and Biopsy

Not routinely required for diagnosis but may be useful when:

  • Cytopenias are unexplained

  • Treatment response needs assessment

-Cytogenetic & Molecular Studies

Assess prognosis:

  • del(13q) – favorable

  • Trisomy 12

  • del(11q)

  • del(17p)/TP53 mutation – poor prognosis

  • IGHV mutation status

Additional Investigations

  • LDH

  • Beta-2 microglobulin

  • Immunoglobulin levels

  • Direct Coombs test (if AIHA suspected)

  • CT scan for staging when indicated

Diagnosis

Diagnosis is based on:

  • Persistent B-cell lymphocytosis (≥5 × 10⁹/L)
  • Characteristic peripheral blood film
  • Flow cytometry confirming monoclonal B-cell CLL phenotype
  • Cytogenetic and molecular testing for prognosis
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Management

–Early-Stage Asymptomatic Disease

  • Active surveillance (“Watch and Wait”)

  • Regular follow-up with CBC and physical examination

Indications for Treatment

  • Progressive bone marrow failure

  • Symptomatic lymphadenopathy or splenomegaly

  • Constitutional (B) symptoms

  • Rapid lymphocyte doubling time

  • Autoimmune cytopenias refractory to corticosteroids

Targeted Therapy

Preferred first-line options for many patients:

  • Bruton’s tyrosine kinase (BTK) inhibitors

    • Ibrutinib

    • Acalabrutinib

    • Zanubrutinib

  • Venetoclax (BCL-2 inhibitor) ± Obinutuzumab

Immunotherapy

  • Anti-CD20 monoclonal antibodies:

    • Rituximab

    • Obinutuzumab

-Chemotherapy

Used less commonly than in the past but may be appropriate in selected patients:

  • Fludarabine

  • Cyclophosphamide

  • Bendamustine

-Supportive Care

  • Infection prevention

  • Vaccination

  • Immunoglobulin replacement in selected patients with recurrent infections

  • Blood transfusions if needed

  • Management of autoimmune complications

Complications

  • Recurrent infections
  • Autoimmune hemolytic anemia
  • Immune thrombocytopenia
  • Bone marrow failure
  • Hypogammaglobulinemia
  • Richter transformation (to diffuse large B-cell lymphoma)
  • Secondary malignancies
  • Tumor lysis syndrome (during treatment)

Prognosis

The prognosis of Chronic Lymphocytic Leukemia (CLL)  varies widely depending on genetic abnormalities and disease stage. Many patients have an indolent disease course and live for years without treatment. Poor prognostic factors include TP53 mutation, del(17p), and unmutated IGHV. Modern targeted therapies have significantly improved survival and quality of life.++

Key Points / Clinical Pearls

  • Chronic Lymphocytic Leukemia (CLL) is the most common adult leukemia in Western countries.
  • It is characterized by the accumulation of mature but functionally abnormal B lymphocytes.
  • Many patients are asymptomatic at diagnosis.
  • Peripheral blood film shows smudge cells.
  • Flow cytometry confirms the diagnosis (CD5+, CD19+, CD23+ B cells).
  • del(17p)/TP53 mutation is associated with a poor prognosis.
  • Early asymptomatic disease is managed with Watch and Wait.
  • BTK inhibitors and Venetoclax-based regimens are the preferred treatments for many patients requiring therapy.
  • Richter transformation is a serious complication.
  • Prognosis depends on disease stage and molecular risk factors.