Prognostic markers and their clinical applicability in chronic lymphocytic leukemia: where do we stand?

Figures & data

Table I. Overview of prognostic markers in CLL.

Prognostic marker*	Prognostic indication	Clinical and/or biological relevance	Evaluation method	Relation to IGHV gene mutation status
Clinical markers
Rai staging (0–IV)	Low stage: low risk; high stage: high risk	Tumor burden	Physical examination and laboratory tests	High stage correlates to UM IGHV genes
Binet staging (A–C)	Low stage: low risk; high stage: high risk	Tumor burden	Physical examination and laboratory tests	High stage correlates to UM IGHV genes
LDT	Short LDT (< 6 months): high risk	CLL cell proliferation rate (disease aggressiveness)	Sequential absolute lymphocyte counts
LDH serum level	High level: high risk	Tumor burden	LDH serum level
B2M serum level	High level: high risk	Tumor burden	B2M serum level
TK serum level	High level: high risk	CLL cell proliferation rate	TK serum level	Elevated serum TK correlates to UM IGHV genes
Genetic markers
IGHV gene mutation status	M IGHV genes: low risk; UM IGHV genes: high risk	Presence or absence of somatic mutations in IGHV genes relates to CLL pathogenesis	IGHV gene sequencing	NA
IGHV gene stereotypy	Different depending on subset: subset 1: high risk; subset 4: low risk	Stereotyped B cell receptors indicate antigen selection in CLL pathogenesis	IGHV gene sequencing	Subset 1 patients carry UM IGHV genes, subset 4 carry M IGHV genes
Absence of known recurrent aberrations	Low risk	Indicates other factors driving disease	FISH or microarray	M IGHV genes
del(11q)	Intermediate to high risk	Deregulation of ATM, BIRC3 and/or other candidate genes	FISH or microarray	UM IGHV genes
del(13q)	Low risk	Deregulation of miR15a/16-1 and/or other candidate genes	FISH or microarray	M IGHV genes
del(17q) and TP53 mutations (deleterious)	High risk	Deregulation of TP53 pathway and lost cell-cycle regulation	FISH, microarray and mutational screening	UM IGHV genes
Trisomy 12	Intermediate prognosis	Unknown function/role	FISH or microarray	UM IGHV genes
Translocations	High risk	Translocation of BCL2, BCL3 or other genes to IG gene promoter region	FISH or cytogenetics	Some translocations, e.g. t(14;19)(q32;q13) correlate to UM IGHV genes
Genomic complexity	High risk	Loss of cell cycle regulation promotes acquisition of novel aberrations	Microarray or cytogenetics	UM IGHV genes
NOTCH1 mutations (activating)	Intermediate to high risk	Constitutively active NOTCH1 promotes proliferation, e.g. through NF-κB signaling	Mutational analysis	UM IGHV genes
SF3B1 mutations (deleterious)	Intermediate to high risk	Truncated SF3B1 unable to function in spliceosome machinery leads to aberrant splicing	Mutational analysis	No relation
BIRC3 mutations (deleterious)	High risk	Non-functional BIRC3 leads to enhanced NF-κB signaling through loss of negative regulation of IKK complex	Mutational analysis	UM IGHV genes
Protein and RNA expression markers
CD38 level	High level: high risk	High expression allows enhanced cell–cell interaction and/or enzyme activity	Flow cytometry	High protein level is correlated to UM IGHV genes
ZAP70 level	High level: high risk	High expression due to enhanced BcR signaling	Flow cytometry or RNA expression	High expression/protein level is correlated to UM IGHV genes
LPL level	High level: high risk	Function of LPL in CLL is unknown	RNA expression	High expression level is correlated to UM IGHV genes
CLLU1 level	High level: high risk	Function of CLLU1 is not known and there is no functional protein	RNA expression	High expression level is correlated to UM IGHV genes
Expression of miRNAs	Different indication depending on miRNA analyzed	Several miRNAs have been found to regulate several genes previously known to be deregulated in CLL	mRNA expression	Certain prognostic markers are correlated to IGHV gene mutation status

CLL, chronic lymphocytic leukemia; LDT, lymphocyte doubling time; LDH, lactate dehydrogenase; B2M, β₂-microglobulin; TK, thymidine kinase; IGHV, immunoglobulin heavy chain variable; M, mutated; UM, unmutated; LPL, lipoproteinlipase; NF-κB, nuclear factor κB; BcR, B cell receptor; NA, not applicable.

*Prognostic markers stated in table are ordered as they appear in text. Subset 1 patients express IGHV1/5/7 clan genes combined with IGKV1-39/IGKV1D-39 genes, subset 4 patients express IGHV4-34/IGKV2-30 genes.

Figure 1. Different molecular mechanisms driving IGHV-mutated and unmutated CLL. An illustration of the most important genetic, RNA and protein based prognostic markers in relation to the IGHV gene mutational status. NOTCH1 activating mutations and BIRC3 disrupting mutations lead to enhanced NF-κB signaling and proliferation in IGHV-unmutated CLL. ZAP70 is involved in BcR signaling and its overexpression leads to enhanced proliferation through, e.g. NF-κB signaling. Disruption of TP53 through deletion and/or mutation is more common in IGHV-unmutated CLL and leads to dysfunctional cell cycle arrest resulting in enhanced cell survival. Although the reason for higher LPL and CLLU1 expression in CLL is unknown, these markers are correlated to high risk.

Figure 2. Overall survival in patients according to known recurrent aberrations (A) and in relation to increasing genomic complexity (B) in a population-based Scandinavian CLL cohort.

Figure 3. Prognostic impact of TP53 aberrations, NOTCH1 and SF3B1 mutations on overall survival and time to treatment in newly diagnosed CLL. For analysis of overall survival (A), six cases with concurrent del(17p) and NOTCH1 or SF3B1 mutations were included in the “TP53 aberration” subgroup, whereas for time to treatment analysis (B), five cases included in the “TP53 aberration” subgroup also displayed NOTCH1 or SF3B1 mutations. There were no statistically significant differences when comparing the TP53 aberration subgroup to either NOTCH1 or SF3B1 mutation subgroups for either overall survival or time to treatment.

Figure 4. LPL expression status and clinical outcome in CLL. Overall survival (A) and time to treatment (B) according to LPL expression status in a newly diagnosed population-based CLL cohort. (C, D) Patients with good cytogenetic markers, i.e. absence of the known recurrent genomic aberrations or presence of del(13q) from the same cohort. In the patient group with good-risk cytogenetic markers, overall survival (C) and time to treatment (D) are stratified by LPL expression status. The expression cut-off for LPL was defined using receiver operating characteristic (ROC) curve analysis and median survival.