Chronic Lymphocytic Leukemia (CLL)
Indolent monoclonal proliferation of mature CD5+ B lymphocytes — most common adult leukemia in Western countries.
Also known as: CLL, chronic lymphocytic leukemia, small lymphocytic lymphoma, SLL
Overview
Mature B-cell neoplasm characterized by clonal proliferation and accumulation of small CD5+ CD19+ CD23+ B lymphocytes in peripheral blood, bone marrow, and lymphoid tissues. CLL and small lymphocytic lymphoma (SLL) are the same disease distinguished by site (CLL has ≥5,000 monoclonal B cells/μL in peripheral blood; SLL is tissue-predominant).
Epidemiology
Most common adult leukemia in the United States and Europe (rare in Asia). Median age at diagnosis ~70 years. Male predominance (~2:1). Annual US incidence ~5 per 100,000. Often asymptomatic and discovered on routine CBC.
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Risk factors
- Age >50
- Male sex
- European ancestry
- Family history (~8x increased risk in first-degree relatives — strongest familial predisposition of any hematologic malignancy)
- Monoclonal B-cell lymphocytosis (MBL) — precursor state with <5,000/μL clonal cells; ~1-2% annual progression risk to CLL
- No clear environmental cause; Agent Orange exposure (recognized by VA)
Pathophysiology
Clonal CD5+ B cells accumulate due to defective apoptosis (BCL-2 overexpression) and chronic B-cell receptor (BCR) signaling. Antigen drive and microenvironmental signals (BTK, PI3K, NF-κB pathways) sustain the clone. The malignant cells are functionally incompetent, producing hypogammaglobulinemia and immune dysfunction. Common cytogenetic abnormalities (FISH panel): del(13q) (favorable, most common), trisomy 12 (intermediate), del(11q) (ATM, adverse), del(17p) (TP53, very adverse).
Clinical presentation
Symptoms
- Often asymptomatic — discovered on incidental lymphocytosis (60-70% of cases)
- Painless lymphadenopathy — cervical, axillary, inguinal
- Constitutional B symptoms in advanced disease: fevers, drenching night sweats, unintentional weight loss >10% in 6 months, severe fatigue
- Early satiety, abdominal fullness from splenomegaly
- Recurrent infections from hypogammaglobulinemia (sinopulmonary, encapsulated organisms)
- Autoimmune cytopenias: warm autoimmune hemolytic anemia, immune thrombocytopenia, pure red cell aplasia
- Bleeding from thrombocytopenia or marrow infiltration
- Skin: leukemia cutis (rare)
Signs / physical exam
- Lymphadenopathy (often symmetric, mobile, rubbery)
- Splenomegaly, hepatomegaly
- Pallor (anemia from marrow infiltration or AIHA)
- Petechiae if severe thrombocytopenia
- Findings of recurrent infection
Classic findings
Older patient with incidental lymphocytosis (lymphocytes >5,000/μL with mature small lymphocytes and smudge cells on smear).
Differential diagnosis
- Mantle cell lymphoma — CD5+ B-cell neoplasm but CD23 NEGATIVE; t(11;14) cyclin D1 overexpression; more aggressive; FMC7 positive
- Marginal zone lymphoma — CD5 negative, often splenic or MALT presentation
- Follicular lymphoma — CD10 positive, CD5 negative; t(14;18) BCL2; nodular pattern
- Hairy cell leukemia — Pancytopenia, splenomegaly without lymphadenopathy, BRAF V600E mutation, cells with hair-like cytoplasmic projections
- Prolymphocytic leukemia — >55% prolymphocytes, aggressive, splenomegaly without lymphadenopathy
- Reactive lymphocytosis (viral, pertussis) — Polyclonal by flow, identifiable infection, self-limited
- Monoclonal B-cell lymphocytosis (MBL) — <5,000 monoclonal B cells/μL with CLL phenotype but no other criteria; CLL precursor
Diagnostic workup
Diagnostic criteria
≥5,000 monoclonal B lymphocytes/μL in peripheral blood with characteristic CLL immunophenotype (CD5+ CD19+ CD23+ light chain restricted) for ≥3 months. SLL: tissue-based disease with <5,000/μL circulating cells.
Labs
- CBC — absolute lymphocytosis (≥5,000 monoclonal B cells/μL required for CLL diagnosis); anemia, thrombocytopenia in advanced disease
- Peripheral smear — small mature lymphocytes with clumped chromatin and scant cytoplasm; SMUDGE (BASKET) CELLS characteristic (fragile cells crushed during smear preparation)
- Flow cytometry — CLL phenotype: CD5+, CD19+, CD20 (dim), CD23+, light chain restriction (kappa or lambda), CD79b dim
- FISH panel — del(13q), trisomy 12, del(11q) ATM, del(17p) TP53 — prognostic; del(17p) treatment-altering
- TP53 sequencing for mutations (treatment selection)
- IGHV mutational status — mutated (favorable) vs unmutated (unfavorable)
- Direct antiglobulin test (DAT) for autoimmune hemolysis screen
- Quantitative immunoglobulins — hypogammaglobulinemia common
- Beta-2 microglobulin (prognostic)
- Bone marrow biopsy not required for diagnosis; reserved for unexplained cytopenia evaluation
- Rai or Binet staging based on lymphocytosis, lymphadenopathy, organomegaly, anemia, thrombocytopenia
Imaging
- CT chest/abdomen/pelvis at diagnosis for baseline lymphadenopathy assessment and before therapy
- PET/CT if Richter transformation suspected (sudden enlargement of one node or B symptoms)
Diagnostic algorithm
| Rai Stage | Findings | Median Survival (untreated, pre-targeted era) |
|---|---|---|
| 0 (Low risk) | Lymphocytosis only | >10 years |
| I (Intermediate) | Lymphocytosis + lymphadenopathy | ~8 years |
| II (Intermediate) | Lymphocytosis + hepatomegaly or splenomegaly (± LAD) | ~6 years |
| III (High) | Lymphocytosis + anemia (Hb <11) | ~2-4 years |
| IV (High) | Lymphocytosis + thrombocytopenia (Plt <100K) | ~2-4 years |
Treatment
First-line
- Indications for treatment (iwCLL criteria) — DO NOT TREAT asymptomatic early-stage disease (Binet A or Rai 0-II without symptoms) — observation is standard; treatment indicated for symptomatic/progressive disease, threatening lymphadenopathy or organomegaly, rapid lymphocyte doubling time (<6 months), B symptoms, autoimmune cytopenias unresponsive to steroids, marrow failure (Hb <10, plt <100)
- BTK inhibitors — ibrutinib, acalabrutinib, zanubrutinib — first-line for most CLL patients including del(17p)/TP53 mutated disease; second-generation BTKis (acala, zanu) have improved cardiac safety (less afib, hypertension)
- Venetoclax (BCL-2 inhibitor) + obinutuzumab (anti-CD20) — fixed-duration 12-month regimen, deep responses including MRD negativity (CLL14 trial)
- Chemoimmunotherapy (FCR fludarabine + cyclophosphamide + rituximab; BR bendamustine + rituximab) — historical first-line; now reserved for selected younger fit IGHV-mutated patients without del(17p)/TP53
Second-line / adjunct
- Venetoclax + rituximab — relapsed CLL (MURANO trial)
- PI3K inhibitors — idelalisib, duvelisib — less commonly used due to toxicity (colitis, pneumonitis, hepatotoxicity, infection); reserved for multiply relapsed
- Pirtobrutinib — non-covalent BTK inhibitor for BTK C481-mutated resistance
- Allogeneic HSCT — selected high-risk relapsed/refractory disease (rare in TKI era)
- CAR-T cell therapy — lisocabtagene maraleucel approved for relapsed/refractory CLL (TRANSCEND CLL 004)
- Supportive care: IVIG for recurrent infection with hypogammaglobulinemia, vaccinations (avoid live vaccines), PJP prophylaxis with chemoimmunotherapy or PI3Ki
- Manage autoimmune cytopenias: prednisone first, rituximab second
Complications
- Recurrent bacterial infections (encapsulated organisms — pneumococcus, H. flu); opportunistic infections (PJP, fungal) in heavily treated
- Autoimmune cytopenias (warm AIHA, ITP, pure red cell aplasia)
- Hypogammaglobulinemia — major contributor to morbidity and mortality
- Richter transformation (~5-10%) — aggressive diffuse large B-cell lymphoma; sudden node enlargement, B symptoms, elevated LDH; poor prognosis
- Second malignancies (skin cancer especially, increased rates)
- Tumor lysis syndrome with venetoclax (dose ramp-up over 5 weeks)
- BTK inhibitor toxicities: atrial fibrillation, hypertension, bleeding, diarrhea, infections; acalabrutinib and zanubrutinib have improved profile vs ibrutinib
- Anemia (multifactorial: marrow infiltration, autoimmune, treatment)
PANCE pearls
- Smudge cells (basket cells) on peripheral smear in an older adult with absolute lymphocytosis are nearly diagnostic of CLL.
- CLL is the only major leukemia where observation ('watch and wait') is the standard of care for early-stage asymptomatic disease — early treatment does not improve survival.
- del(17p) / TP53 mutation: very adverse prognosis with chemoimmunotherapy; standard care is BTK inhibitor or venetoclax-based therapy (NOT chemoimmunotherapy).
- IGHV mutational status is a major prognostic factor — mutated favorable, unmutated unfavorable.
- Hypogammaglobulinemia → recurrent encapsulated organism infections; vaccinate against pneumococcus, influenza, meningococcus, and consider IVIG for severe recurrent infection.
- Richter transformation — sudden development of aggressive lymphoma (DLBCL most commonly) in CLL; clue is rapid node growth and B symptoms; biopsy diagnostic; PET shows high SUV.
- Venetoclax requires tumor lysis prophylaxis with stepwise dose escalation over 5 weeks plus hydration, allopurinol/rasburicase, and frequent labs.
- Ibrutinib causes atrial fibrillation and bleeding (especially with anticoagulants); newer BTKis (acalabrutinib, zanubrutinib) have lower rates.
References
- iwCLL 2018 — iwCLL guidelines for diagnosis, indications for treatment, response assessment, and supportive management of CLL (Hallek et al., Blood 2018)
- CLL14 — Venetoclax-Obinutuzumab for Previously Untreated Chronic Lymphocytic Leukemia (Fischer et al., NEJM 2019)
- RESONATE — Ibrutinib versus Ofatumumab in Previously Treated CLL (Byrd et al., NEJM 2014)
- MURANO — Venetoclax-Rituximab in Relapsed or Refractory CLL (Seymour et al., NEJM 2018)
- ELEVATE-TN — Acalabrutinib with or without obinutuzumab versus obinutuzumab + chlorambucil in treatment-naive CLL (Sharman et al., Lancet 2020)
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