Cytogenetic findings in WHO-defined polycythaemia vera and their prognostic relevance
Polycythaemia vera (PV) is a myeloproliferative neoplasm (MPN) that is characterized by increased red cell mass and JAK2 mutations (Tefferi & Pardanani, 2015). Median survival in PV is approximately 14 years although it approaches 24 years in patients younger than age 60 years (Tefferi et al, 2014). The international working group for MPN research and treatment (IWG-MRT) has studied over 1500 patients with World Health Organization (WHO)-defined PV, and identified advanced age, leucocytosis and abnormal karyotype as independent risk factors for overall survival (OS) and leukaemia-free survival (LFS)(Tefferi et al, 2013). In addition, occurrence of venous thrombosis was identified as a risk factor for OS (Tefferi et al, 2013). Most recently, the possibility of additional prognostic information in PV from adverse somatic mutations (ASXL1, SRSF2 and IDH2) was reported (Tefferi et al, 2016). The objective of the current study was to carefully analyse the independent prognostic effect of cytogenetic information in PV, in terms of OS, LFS, myelofibrosis-free survival (MFFS) and thrombosis-free survival (TFS), in the context of other previously established risk factors, including adverse somatic mutations.
The current study was approved by the institutional review board of Mayo Clinic (Rochester, MN). Study patients fulfilled the 2016 WHO criteria for the diagnosis of PV (Arber et al, 2016) with cytogenetic information available at time of diagnosis. Cytogenetic analysis and reporting was done according to the International System for Human Cytogenetic Nomenclature (Simons et al, 2013). Mutation screening for adverse mutations, including ASXL1, SRSF2 and IDH2, was performed as previously described (Tefferi et al, 2016). Assignment as “unfavourable karyotype” was according to criteria established for primary myelofibrosis (PMF) (Caramazza et al, 2011). Differences in the distribution of continuous variables between categories were analysed by either Mann-Whitney or Kruskal–Wallis test. Patient groups with nominal variables were compared by χ2-test. OS analysis was considered from the date of diagnosis to date of death or last contact. MFFS, LFS and TFS were determined from the time of diagnosis to the time of event occurrence after diagnosis. All survival curves were prepared by the Kaplan-Meier method and compared by the log-rank test. Cox proportional hazard regression model was applied for multivariate analysis. P-values less than 0·05 were considered significant. The Stat View (SAS Institute, Cary, NC, USA) statistical package was used for all calculations.
A total of 196 patients (51% females), with a median age of 64 years were considered. Table 1 outlines the presenting clinical and laboratory features of the study patients. Cytogenetic information is included in Table 2, which shows an incidence of 19% for abnormal karyotype, 4% for unfavourable karyotype, 17% for sole abnormalities, 2% for two or more abnormalities and 0% for complex karyotype. The most frequent sole abnormalities were +9 (5%), Loss of Y (4%), +8 (3%) and del(20q) (3%) while other sole abnormalities were seen in single patients (Table 2); the specific abnormalities seen in the four patients with two abnormalities are also listed in Table 2. Comparison of patients with and without abnormal karyotype displayed similar presenting features, with the exception of a lower platelet count in patients with abnormal karyotype (P = 0·04); ASXL1 mutational frequency was also similar between the two groups (15% vs. 12%) whereas a single patient with abnormal karyotype, displayed SRSF2 mutation (Table 1).
| Variables | All patients (n = 196) | Patients with abnormal karyotype (n = 38, 19%) | Patients with normal karyotype (n = 158, 81%) | P value |
|---|---|---|---|---|
| Age at referral; median (range), years | 64 (17–94) | 65 (30–94) | 63 (17–90) | 0·2 |
| Age >60 years, N (%) | 112 (57%) | 26 (68%) | 86 (54%) | 0·12 |
| Female | 100 (51%) | 15 (39%) | 85 (54%) | 0·11 |
| Haemoglobin, g/l; median (range) | 177 (154–240) | 178 (157–217) | 177 (154–240) | 0·5 |
| Platelet count, ×109/l; median (range) | 467 (37–2747) | 389 (37–862) | 487 (113–2747) | 0·035 |
| WBC, ×109/l; median (range) | 11·7 (4·3–59·3) | 12·4 (5·5–30·2) | 11·4 (4·3–59·3) | 0·65 |
| WBC ≥11 × 109/l, N (%) | 111 (58%) | 21 (58%) | 90 (58%) | 0·9 |
| WBC ≥15 × 109/L, N (%) | 41 (21%) | 10 (28%) | 31 (20%) | 0·3 |
| Palpable splenomegaly (N evaluable = 183) | 42 (23%) | 10 (29%) | 32 (21%) | 0·3 |
| Presence of pruritus | 54 (28%) | 11 (29%) | 43 (27%) | 0·8 |
| Presence of microcirculatory disturbances (N evaluable = 189) | 64 (34%) | 12 (32%) | 52 (34%) | 0·8 |
| Presence of erythromelagia (N evaluable = 195) | 12 (6%) | 2 (5%) | 10 (6%) | 0·8 |
| History of hypertension (N evaluable = 194) | 98 (51%) | 20 (54%) | 78 (50%) | 0·6 |
| History of hyperlipidaemia | 57 (29%) | 13 (34%) | 44 (28%) | 0·4 |
| History of diabetes | 19 (10%) | 4 (11%) | 15 (9%) | 0·8 |
| Active tobacco users (N evaluable = 195) | 19 (10%) | 3 (8%) | 16 (10%) | 0·7 |
| History of thrombosis | 64 (33%) | 13 (34%) | 51 (32%) | 0·82 |
| ASXL1 mutated (N evaluable = 69) | 9 (13%) | 2 (15%) | 7 (12%) | 0·78 |
| SRSF2 mutated (N evaluable = 69) | 1 (1%) | 1 (8%) | 0 (0%) | 0·037 |
| IDH2 mutated (N evaluable = 69) | 0 | 0 | 0 | 1·0 |
- WBC, white blood count.
- Bold font indicates significant p-values
| N (%) | Effect on overall survival (P value) | Effect on fibrosis-free survival (P value) | Effect on leukaemia-free survival (P value) | Effect on thrombosis-free survival (P value) | |
|---|---|---|---|---|---|
| Total | 196 (100%) | ||||
| Abnormal | 38 (19%) |
0·03 HR 1·95, 95% CI 1·06–3·57 |
0·0002 HR 7·80, 95% CI 2·65–22·98 |
0·0037 HR 12·53, 95% CI 2·27–69·22 |
0·37 |
| Unfavourable | 7 (4%) |
0·003 HR 4·23, 95% CI 1·64–10·91 |
0·17 |
0·017 HR 29·26, 95% CI 1·82–469·63 |
NA |
| Sole abnormalities | 34 (17%) |
0·018 HR 2·14, 95% CI 1·14–4·01 |
0·0008 HR 6·75, 95% CI 2·21–20·63 |
0·009 HR 11·10, 95% CI 1·83–67·39 |
0·5 |
| +9 | 9 (5%) | NA |
0·0002 HR 10·77, 95% CI 3·10–37·38 |
NA | 0·87 |
| Loss of Y | 8 (4%) |
0·0001 HR 5·58, 95% CI 2·33–13·35 |
NA |
0·014 HR 22·20, 95% CI 1·85–265·99 |
0·86 |
| +8 | 5 (3%) | 0·076 | 0·14 |
0·017 HR 29·26, 95% CI 1·82–469·63 |
NA |
| del(20q) | 5 (3%) | 0·33 | 0·15 |
0·022 HR 25·31, 95% CI 1·58–405·03 |
NA |
| +13 ps | 1 (0·5%) | NA | NA | NA | NA |
| del(11q) | 1 (0·5%) | NA | NA | NA | NA |
| inv(1) | 1 (0·5%) | NA | NA | NA | NA |
| inv(2) | 1 (0·5%) | NA | NA | NA | NA |
| inv(4) | 1 (0·5%) | NA | NA | NA | NA |
| t(9;18) | 1 (0·5%) | NA | NA | NA | NA |
| del(13q) | 1 (0·5%) | NA | NA | NA | NA |
| Two abnormalities | 4 (2%) | 0·9 |
0·02 HR 12·80, 95% CI 1·53–107·15 |
0·009 HR 25·63, 95% CI 2·24–293·80 |
NA |
| +9 and del(13q) | 1 (0·5%) | NA | NA | NA | NA |
| Loss of Y and del(20q) | 1 (0·5%) | NA | NA | NA | NA |
| Add(9)(p22)der(9)(p22q)add(p22) and mar | 1 (0·5%) | NA | NA | NA | NA |
| del(20q) and t(X;11) | 1 (0·5%) | NA | NA | NA | NA |
- 95% CI, 95% confidence interval; HR, Hazard ratio; NA, not applicable because the number of informative cases was too small to allow valid statistical analysis.
After a median follow-up of 84 months, 62 (32%) deaths, 6 (3%) leukaemic transformations, 16 (8%) fibrotic progressions and 36 (18%) thrombotic events were recorded. In univariate analysis, abnormal karyotype adversely affected OS [P = 0·03; Hazard ratio (HR) 2·0, 95% confidence interval (CI) 1·1–3·6], LFS (P = 0·0002; HR 7·8, 95% CI 2·7–23·0) and MFFS (P = 0·004; HR 12·5, 95% CI 2·3–69·2) but not TFS (P = 0·4) (Table 2); inferior outcome, when compared to normal karyotype, was also demonstrated for unfavourable karyotype (OS, P = 0·003; LFS, P = 0·02), sole abnormalities (OS, P = 0·02; LFS, P = 0·009; MFFS, P = 0·0008), +9 (MFFS, P = 0·0002), Loss of Y (OS, P = 0·0001; LFS, P = 0·01) +8 (LFS, P = 0·02), del(20q) (LFS, P = 0·02) and two abnormalities (MFFS, P = 0·02; LFS, P = 0·009).
On multivariate analysis for OS, which included age, leucocyte count, thrombosis and adverse mutations, the detrimental effect of abnormal karyotype (P = 0·04; HR 1·9, 95% CI 1·03–3·6) and loss of Y (P = 0·007; HR 3·4, 95% CI 1·4–8·2) remained significant; other independent risk factors included age >60 years and leucocyte count ≥15 × 109/l, only; the respective HRs (95% CI) were 4·7 (2·5–9·1) and 2·5 (1·5–4·4) in the multivariate analysis that included abnormal karyotype and 2·8 (1·5–5·0) and 2·8 (1·5–5·0) in the analysis that considered loss of Y chromosome. Multivariate P values were of borderline significance for sole abnormalities (P = 0·06) and unfavourable karyotype (P = 0·1). Presence of adverse mutations was significant (P = 0·05) in univariate but not in multivariate analysis that included abnormal karyotype as a covariate. Abnormal karyotype (HR 15·8, 95% CI 2·8–88·9), sole abnormalities (HR 13·2, 95% CI 2·2–80·8) and loss of Y (HR 45·3, 95% CI 2·3–910·3) also remained significant during multivariate analysis for LFS whereas significance for unfavourable karyotype became borderline (P = 0·06). On the other hand, in univariate analysis, cytogenetic abnormalities were the only risk factors for MFFS: abnormal karyotype (P = 0·0002), sole abnormalities (P = 0·0008), two abnormalities (P = 0·02) and +9 (P = 0·0002).
The current study confirms our previously reported observation in PV regarding the adverse effect of abnormal karyotype on OS and LFS (Tefferi et al, 2013). The negative prognostic effect of abnormal karyotype is demonstrated with abnormalities previously deemed favourable namely +9, loss of Y and del(20q). The current study also highlights prognostic independence of abnormal karyotype from adverse mutations in PV (Tefferi et al, 2016). Finally, we suspect that the larger sample size and longer follow-up in the current study may have contributed to these findings (Swolin et al, 1988; Gangat et al, 2008; Sever et al, 2013). Regardless, the demonstration of the significant relevance of abnormal karyotype, not only for OS but also for LFS and MFFS suggests the practical importance of obtaining cytogenetic information at time of diagnosis in PV, and possibly during change in clinical course. The current study also suggests the possibility of refining contemporary prognostic models in PV by incorporating cytogenetic information.
Author contributions
AT designed the study, contributed patients, extracted, analysed data, wrote and approved the final draft of the manuscript; DB and SC extracted, analysed data, wrote and approved the final draft of the manuscript; NG and AP contributed patients, extracted data and approved the final draft of the manuscript; CAH reviewed pathology and approved the final draft of the manuscript; RPK reviewed cytogenetics and approved the final draft of the manuscript.
