A 62-year-old man presents with painless lymphadenopathy and hepatosplenomegaly. Lymph node biopsy shows diffuse infiltration by small lymphocytes with CD5+, CD19+, CD23+ immunophenotype. Serum LDH is mildly elevated. What is the drug of choice for first-line treatment of this condition?

Explanation

## Diagnosis: Chronic Lymphocytic Leukemia (CLL) **Key Point:** The immunophenotype CD5+, CD19+, CD23+ is pathognomonic for CLL. This is the most common leukemia in adults in Western countries. **High-Yield:** First-line treatment of CLL depends on fitness status and disease stage: - **Fit patients with advanced disease (Rai III–IV or Binet C):** Chemoimmunotherapy (FCR or BR) or venetoclax + obinutuzumab - **Unfit or early-stage disease:** Chlorambucil or bendamustine monotherapy - **Elderly/comorbid patients:** Chlorambucil, bendamustine, or single-agent rituximab ### Rationale for Chlorambucil/Bendamustine Given the patient's age (62) and mild LDH elevation (suggesting early-stage disease), **chlorambucil or bendamustine monotherapy** is the preferred first-line choice. These alkylating agents: 1. Are well-tolerated in older patients 2. Have acceptable response rates in early-stage/asymptomatic CLL 3. Avoid the toxicity of intensive chemoimmunotherapy in unfit patients **Clinical Pearl:** Bendamustine has largely replaced chlorambucil in many centers due to superior response rates and tolerability, though both are acceptable. ### Why Other Options Are Not First-Line | Agent | Role in CLL | Why Not First-Line Here | |-------|-------------|------------------------| | Fludarabine | Purine analogue; part of FCR regimen | Myelosuppressive; reserved for fit patients with advanced disease | | Rituximab (anti-CD20) | Monoclonal antibody; synergizes with chemotherapy | Monotherapy has lower response rates; used with chemotherapy (e.g., BR) | | CHOP | Anthracycline-based regimen | Not standard for CLL; causes cardiotoxicity; reserved for Richter transformation | **Mnemonic:** **ABCDE of CLL treatment choice:** - **A**ge and fitness (elderly → monotherapy) - **B**ulky disease (present → combination therapy) - **C**omorbidities (many → avoid intensive regimens) - **D**isease stage (early → monotherapy; advanced → combination) - **E**xcretion/renal function (assess before purine analogues) **High-Yield:** Modern alternatives (venetoclax + obinutuzumab, ibrutinib) are increasingly used, but chlorambucil/bendamustine remain the standard first-line for unfit/early-stage patients.