Rearrangement of NOTCH1 or BCL3 can independently trigger progression of CLL

To the editor:

Recent data indicate that NOTCH1 mutations significantly increase the risk of CLL progression toward Richter syndrome (RS) and chemoresistance,^1,2  and that activation of NOTCH1 at time of CLL diagnosis is an independent prognostic factor of poor survival.^1,3  We report here a case of CLL with a novel rearrangement of NOTCH1 identified at the time of RS. The patient, a 58-year-old male, was diagnosed with CLL (unmutated VH) in RS in June 2003. Cytogenetic analysis and FISH on peripheral blood (PBL), bone marrow (BM), and lymph node (LN) cells showed 2 related clones: one with an isolated +12 and a second with +12 and dic(9;14)(q34;q32) (supplemental Table 1, available on the Blood Web site; see the Supplemental Materials link at the top of the online article). FISH analysis of dic(9;14)(q34;q32) indicated that this aberration resulted in juxtaposition of 3′IGH and 5′NOTCH1, as evidenced by the loss of sequences telomeric to the breakpoints (Figure 1A-D). These imbalances were confirmed by array CGH (data not shown). The targeting of NOTCH1 by dic(9;14) was evidenced by qRT-PCR analysis, which showed a 10-fold up-regulation of NOTCH1 mRNA (Figure 1E) and a low expression of the neighboring genes (GPSM11, CARD9, DNL2). Immunoblotting of a cell lysate from LN with a NOTCH1 antibody recognizing active, cleaved NOTCH1 (Val1744) identified a band corresponding to activated intracellular NOTCH1 (Figure 1F), suggesting an additional truncating mutation. Indeed, sequence analysis identified a 2 basepair deletion, ΔCT7544–7545/P2515fs, in the nucleotide sequence encoding the PEST domain (Figure 1G). This mutation resulting in expression of a truncated intracellular NOTCH1 allele is recurrent in T-ALL⁴  and CLL.^1-3,5 

The patient was treated and achieved complete remission (supplemental Table 1). In 2007, however, CLL relapsed and an examination of BM identified a clone with a sole +12 negative for ΔCT7544–7545/P2515fs. Two years later, CLL progressed and BM revealed an evolved clone with complex aberrations including +12 and t(14;19)(q32;q13)/IGH-BCL3 but lacking dic(9;14)(q34;q32). Of note, BM was again positive for ΔCT7544–7545/P2515fs. Despite treatment, 2 clones harboring +12, one with t(14;19) and a second with new additional karyotypic changes, were seen in the analyzed BM (06/2011) positive for ΔCT7544–7545/P2515fs. TP53 disruption frequently associated with RS⁶  was not observed in the analyzed samples (supplemental Table 1). Four months later, the patient developed peripheral T-cell lymphoma, a rare recurrent event in CLL.⁷  Altogether, the present case allows us to deduce the sequence of multiple genetic defects driving development and progression of CLL. An initial clone with +12, likely present at a presymptomatic CLL phase, later acquired an activating mutation of NOTCH1. Subsequent acquisition of dic(9;14)/IGH-NOTCH1 triggered Richter transformation. After a few years, a persistent, chemorefractory NOTCH1-mutated clone underwent another hit, t(14;19)/IGH-BCL3, which initiated the second progression that was followed by a fatal CLL-unrelated T-cell lymphoma. Our findings confirm the risk of activating mutations of NOTCH1 in Richter transformation of CLL,^1,2  particularly CLL with +12,³  and highlight that a residual chemotherapy-resistant NOTCH1-mutated clone is at risk of acquiring further progression-associated hits. Besides the known t(14;19)(q32;q13)/IGH-BCL3,^8-10  we also identified dic(9;14)(q34;q32)/IGH-NOTCH1, which so far has not been reported in B-cell leukemia/lymphoma, as a novel genomic aberration capable of triggering RS.