A 52-year-old man presents with fatigue and is found to have 8,500 CD5+/CD19+/CD23+ B lymphocytes/μL on flow cytometry. FISH analysis reveals deletion at the locus marked **A** in the diagram. Which of the following best explains the clinical significance of this finding in this patient's chronic lymphocytic leukemia?

Question

Accepted Answer

A. Loss of ATM kinase function impairs DNA double-strand break sensing and p53-mediated DNA damage response, conferring intermediate-to-poor prognosis and reduced chemotherapy sensitivity. ## Why Option 1 is correct

Deletion at 11q22.3 (marked **A**) targets the ATM (Ataxia-Telangiectasia Mutated) gene, which encodes a serine/threonine kinase essential for sensing DNA double-strand breaks and activating p53-mediated DNA damage response. Del(11q) CLL typically involves biallelic ATM inactivation (deletion plus mutation on the remaining allele), resulting in impaired DNA repair and genomic instability. According to the Döhner hierarchical model and iwCLL 2018 guidelines, del(11q) confers intermediate-to-poor prognosis with median survival of 7–9 years in the pre-targeted-therapy era. Critically, ATM-deficient CLL shows reduced response to fludarabine-based chemotherapy, though BTK inhibitors (ibrutinib, acalabrutinib) and BCL2 inhibitors (venetoclax) effectively overcome this adverse biology.

## Why each distractor is wrong

- **Option 2**: Describes del(13q14) at the DLEU2 locus (marked **C**, not **A**). Del(13q) is the most common FISH abnormality in CLL and confers favorable prognosis with median survival >15 years—the opposite of del(11q).
- **Option 3**: Describes del(17p13)/TP53 mutation (marked **B**, not **A**). While TP53 deletion is the highest-risk cytogenetic abnormality with median survival <3 years, the question specifically asks about the locus marked **A** (11q22.3).
- **Option 4**: Describes trisomy 12 (marked **D**, not **A**). Trisomy 12 confers intermediate prognosis but does not involve ATM loss and has different pathogenic mechanisms and treatment implications than del(11q).

**High-Yield:** Del(11q) CLL = ATM loss → impaired DNA repair → intermediate-to-poor prognosis → reduced fludarabine sensitivity but responsive to BTK/BCL2 inhibitors.

[cite: iwCLL Guidelines 2018; NCCN CLL 2024; Döhner et al. Prognostic Significance of Genetic Abnormalities in CLL]

Answer

B. Gain of chromosome 12 material confers intermediate prognosis equivalent to del(11q) with similar treatment outcomes

Answer

C. Loss of TP53 function represents the highest-risk cytogenetic abnormality with median survival <3 years

Answer

D. Loss of DLEU2 tumor suppressor results in favorable prognosis with median survival exceeding 15 years

Explanation

Why Option 1 is correct

Why each distractor is wrong

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