CLL; Assessment of prognosis

In chronic lymphocytic leukaemia, a third of patients never need treatment and have long survival; in another third, an initial indolent phase is followed by disease progression; the remaining third exhibit aggressive disease at onset and need immediate treatment.[95] The Rai and Binet staging systems have enabled individuals with chronic lymphocytic leukaemia to be divided into three prognostic groups (good, intermediate, and poor) and have provided a foundation for clinicians to design therapeutic strategies for the disease. However, with neither the Rai nor the Binet staging system can we predict who in the good prognosis group will develop progressive disease.[96] Several attempts have been made to address this deficiency. Lymphocyte doubling time, the pattern of bone-marrow involvement, and concentrations in serum of β2 microglobulin, thymidine kinase, and soluble CD23 all have some value but also important drawbacks.[97] Lymphocyte counts can double in response to infection, vaccination, and steroid treatment; patterns of marrow involvement need invasive investigation; measurement of thymidine kinase in serum needs a radioassay; and amounts of CD23 and β2 microglobulin indicate both bulk of disease and rates of progression.

As reported above in the section on Genetic abnormalities, chronic lymphocytic leukaemias with mutated immunoglobulin genes have good prognosis and those with unmutated genes show poor prognosis.[67], [68] and [98] The mutational profile of immunoglobulin genes delineates prognostic groups within all Binet's stages.[67] and [99] The IGHV mutational profile has the advantage that it remains constant during clonal evolution, which contrasts with genomic aberrations and serum markers. Since sequencing IGHV genes is seen as costly and time consuming (though this is probably not true), and it is unavailable at most medical facilities, detection of appropriate, reliable surrogate markers for IGHV mutational status has attracted worldwide attention.

An early candidate surrogate marker was expression of CD38. However, although CD38 expression is associated with poor prognosis, its relation to immunoglobulin mutational status remains controversial.[68] and [100] Furthermore, expression of CD38 can change during disease evolution and concerns exist with respect to interlaboratory variations and the definition of the best cutoff value.[97] and [101]

Crespo and colleagues [102] developed a multivariable flow-cytometric test for ZAP70 that showed 95% correlation with IGHV gene mutational status; this finding was confirmed by a similar assay that used a slightly different way of expressing the results.[103] However, these tests used indirect immunofluorescence, and a more convenient assay using direct immunofluorescence gave only 77% concordance with mutational status of IGHV genes.[104] With the direct assay, ZAP70 seemed to be superior to IGHV genes in prediction of time-to-first treatment, whereas in ZAP70-negative patients, IGHV mutational status delineated good from intermediate prognosis.104 So far, this assay has not exported well to other laboratories and considerable dispute remains about how ZAP70 amounts should be estimated.[105]

LPL is consistently overexpressed in patients with unmutated chronic lymphocytic leukaemia and has also been proposed as a surrogate marker.[106] By contrast with ZAP70, which sometimes fails to identify advanced forms of disease, this marker seems to be an independent prognostic factor for individuals with Binet stage B and C disease.[106] and [107] Assay by real-time quantitative PCR is less widely applicable than flow cytometry, but data suggest that this method is as good as IGHV mutational analysis and more reliable than ZAP70 as a prognostic factor.[108]

For laboratories with facilities to measure concentrations in serum of thymidine kinase, high amounts at diagnosis identified patients categorised into good prognosis groups by other biomarkers (IGHV, ZAP70, CD38, del13q14) who subsequently progressed to advanced disease.[109] Measurement of telomere length also refined the prognostic analysis of IGHV unmutated cases. Patients with short telomeres had significantly shorter progression-free and overall survival than did those with long telomeres.[110] Low amounts of the chemokine receptor CXCR3 predict reduced survival independent of IGHV mutations and CD38 levels.[111] The degree of upregulation of CLLU1 is an independent prognostic marker in patients younger than age 70 years.[112]

Although all these markers provide useful prognostic information, the mutational status of IGHV genes and del 17p and del 11q are the most robust prognostic indicators, having been validated in prospective phase III clinical trials. Findings of a US Intergroup study comparing fludarabine with fludarabine plus cyclophosphamide[113] showed that median progression-free survival was significantly lower for patients with del 17p13 or del 11q23 than for those with other cytogenetic findings. Although progression-free survival was longer for individuals with mutated IGHV genes than for those with unmutated genes, the study was insufficiently powered for this finding to reach significance.[113] In the UK Leukaemia Research Fund CLL4 trial comparing fludarabine, fludarabine plus cyclophosphamide, and chlorambucil, the effect of prognostic markers on outcome was assessed prospectively.[114] Importantly, prognostic factors had a greater effect on overall survival than did choice of treatment. Patients with del 17p in more than 20% of cells had a significantly poorer response rate and median overall survival than did all other individuals, whereas those with unmutated IGHV genes or del 11q23 had significantly shorter progression-free and overall survival than did those with mutated IGHV genes, no matter which treatment they were given. Findings of a CALGB 9712 phase II comparison of different schedules of rituximab given with fludarabine [115] showed that median progression-free and overall survival were significantly greater in patients with mutated IGHV genes than in those with unmutated genes. Survival was also significantly increased with the Döhner hierarchical classification of FISH results moving from del 17p13 to del 13q14.

Combinations of prognostic factors might be more useful than individual factors. CD38 and IGHV mutations100 or CD38 and ZAP70[116] and [117] both perform better than any one factor. A scoring system based on six surface molecules (CD62L [SELL], CD54 [ICAM1], CD49c [ITGA3], CD49d [ITGA4], CD38, and CD79B) detectable by flow cytometry has been proposed.118 Another using the easily available factors of age, sex, Rai stage, number of lymph nodes involved, absolute lymphocyte count, and β2 microglobulin has been assessed in many patients.[119]

By multivariate analysis, both Binet staging and IGHV genes retain their independent prognostic significance in chronic lymphocytic leukaemia and are complementary.[67] and [99] As table 2 shows, addition of Binet staging to the mutational profile of immunoglobulin genes and 17p13 deletion, which is the strongest independent prognostic marker, allows segregation of patients into five prognostic subgroups. We do not claim this prognostic system to be definitive; undoubtedly incorporation of other factors will give greater refinement, but it makes use of the best established and validated factors.

In conclusion, recognition of novel biological variables has had a major effect on our understanding of chronic lymphocytic leukaemia. Some variables seem to be of considerable prognostic importance but, as yet, no evidence is available to suggest that changing therapeutic approaches on the basis of these results will lead to improvement in outcome. Prospective clinical trials are needed to address the stratification of patients according to these factors.

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