Cytogenetic profile of 1791 adult acute myeloid leukemia in India

Background Cytogenetic analysis continues to have an important role in the management of acute myeloid leukemia (AML) because it is essential for prognostication. It is also necessary to diagnose specific categories of AML and to determine the most effective form of treatment. Reports from South Asia are few because the availability of cytogenetic services is relatively limited. Methods We performed a retrospective analysis of the cytogenetic findings in adults with AML seen consecutively in a single centre in India. The results were categorised according to the 2022 World Health Organisation (WHO), International Consensus Classification (ICC) and European LeukemiaNet (ELN) classifications. Results There were 1791 patients aged 18–85 years (median age 42, 1086 males). Normal karyotypes were seen in 646 (36%) patients. The 1145 (64%) abnormal karyotypes comprised 585 (32.7%) with recurrent genetic abnormalities (RGA), 403 (22.5%) with myelodysplasia-related cytogenetic abnormalities (MRC), and 157 (8.8%) with other abnormalities. There were 567 (31.7%) patients with solitary abnormalities and 299 (16.7%) with two abnormalities. Among the 279 (15.6%) patients with ≥ 3 abnormalities, 200 (11.2%) had complex karyotypes (CK) as per the WHO/ICC and 184 (10.3%), as per the ELN definition. There were 158 (8.8%) monosomal karyotypes (MK). Patients with normal karyotypes had a higher median age (45 years) than those with abnormal karyotypes (40 years, p < 0.001), and those with ≥ 3 abnormalities (43 years), than those with fewer abnormalities (39 years, p = 0.005). Patients with CK (WHO/ICC) and monosomal karyotypes had a median age of 48 years. Those with RGA had a lower median age (35 years, p < 0.001) than MRC (46 years) or other abnormalities (44 years). The t(15;17) was the most common abnormality (16.7%),followed by trisomy 8 (11.6%), monosomy 7/del 7q (9.3%), t(8;21) (7.2%), monosomy 5/del 5q (6.7%) and monosomy 17/del 17p (5.2%). Conclusion Our findings confirm the lower age profile of AML in India and show similarities and differences with respect to the frequencies of individual abnormalities compared to the literature. The frequencies of the t(15;17), trisomy 8 and the high-risk abnormalities monosomy 7 and monosomy 5/del 5q were higher, and that of the inv(16), lower than in most reports. Supplementary Information The online version contains supplementary material available at 10.1186/s13039-023-00653-1.


Background
Cytogenetic analysis continues to be an important part of the work up of acute myeloid leukemia (AML) because the chromosomal constitution of a leukemia has a major impact on prognosis [1].It is also essential for the diagnosis of two categories which are based upon the presence of specific cytogenetic abnormalities, namely, AML with recurrent genetic abnormalities (AML-RGA) and AML with myelodysplasia-related cytogenetic changes (AML-MRC) [2][3][4][5][6][7][8].Morphological evidence of dysplasia alone is no longer a criterion for the diagnosis of AML-MRC in the most recent (2022) classifications of AML provided by the World Health Organisation (WHO), The International Consensus Classification of AML (ICC) and the European LeukemiaNet [6][7][8].The pre-treatment karyotype is also used to assign patients to risk groups in order to determine whether standard therapies or more intensive forms of treatment are likely to be most effective [1,9].The presence of multiple abnormalities signifies that there is disease progression [1].Chromosomal abnormalities have been described in over half of AML in adults but the frequency of specific cytogenetic abnormalities varies in different parts of the world [1,10,11].It is also well-documented that the median age of AML patients in Western countries and Japan is about two decades higher than in the rest of the world .Whether this is related to different pathogenic processes or is a reflection of the younger population profile is unclear.Reports of cytogenetic changes in AML from South Asian countries are limited, because a large proportion of patients do not have access to diagnostic technologies other than morphology [29][30][31][32].We describe the chromosomal abnormalities seen in a large group of adult patients with AML diagnosed consecutively at our centre over 15 years and compare our findings with the literature.

Patients
Karyotypes of all patients with AML aged ≥ 18 years seen at the Christian Medical College, Vellore between 2003 and 2017 and who underwent cytogenetic analysis at diagnosis were included in the analysis.Patients who had received chemotherapy and those with normal karyotypes with < 15 analysable metaphases were excluded.

Cytogenetic analysis
Conventional cytogenetic analysis was performed on unstimulated overnight (or 48-h) cultures of bone marrow using standard protocols, and results reported as per the International System for Human Cytogenomic Nomenclature (ISCN) [33,34].Fluorescence in-situ hybridization (FISH) analysis was performed if the bone marrow morphology suggested that a specific abnormality could be present, to confirm a suspected abnormality if the chromosome morphology was suboptimal or to establish base-line values for follow-up post treatment.

Descriptions of abnormalities
We used the terminology and definitions that most resembled the WHO 2016 and earlier classifications of AML for ease of comparison with previous studies because of slight differences between the 2022 WHO, ICC and ELN classifications of AML with respect to the definitions of MRC and complex karyotypes (CK) and the terminology used to describe the subtypes [6][7][8].Therefore, we used the WHO/ICC definitions to describe complex karyotypes (≥ 3 abnormalities in the absence of class-defining RGA) unlike the ELN definition which also excluded hyperdiploid karyotypes without structural abnormalities (≥ 3 trisomies/polysomies only).Even though trisomy 8, monosomy 17 and the del 20q were termed MRC only by the ICC/ELN and the del 11q and del 13q/monosomy 13, only by the WHO, we categorised all these abnormalities as MRC.Monosomal karyotypes (MK) were those with two or more autosomal monosomies, or one single autosomal monosomy in addition to one or more structural chromosome abnormalities other than core-binding factor AML [8].Apart from numerical abnormalities, balanced translocations (t) and unbalanced structural rearrangements were regarded as single abnormalities.Each abnormality in a karyotype was recorded separately to determine its absolute frequency and categorised as RGA, MRC or other.The karyotypes were also categorised hierarchically as described by Moorman et al., with each being assigned to only one of four mutually exclusive groups in the following sequence: translocations, inversions and insertions; deletions and monosomies; trisomies and duplications; normal karyotypes [35].

Statistical analysis
Statistical analysis was performed using STATA 16 (Statcorp).One-way ANOVA was used to compare age differences between groups.We compared our findings with the West (Europe, U.K, USA and Australia), South-East (S.E) Asia (China, Hong Kong, Singapore, Malaysia, South Korea and Japan) and North (N.) Africa (Tunisia, Morocco and Egypt).Weighted average percentages of each abnormality were determined for all three regions (upto 18,850, 8971 and 1646 patients from the West, S.E Asia and N. Africa respectively) and the frequencies compared with our study using the one-sample proportion test.The value p < 0.05 was considered to be significant.

Overview of patient characteristics and cytogenetic abnormalities (Table 1)
There were 1860 patients with adult AML who presented at diagnosis, of whom 1791 (96.3%) fulfilled the criteria for inclusion.Patients ranged from 18-85 years (median 42 years); 1085 (60.6%) were males.Normal karyotypes were seen in 646 patients (36.1%) and were determined by analysis of ≥ 20 metaphases in 89% of patients and 15-19 metaphases in the remaining 11%.There were 1145 (63.9%) patients with abnormal karyotypes.

Age distribution (Table 1, Figs. 1 and 2)
Patients with normal karyotypes had a higher median age than those with abnormal karyotypes (45 vs 40 years, p < 0.001).Patients with ≥ 3 abnormalities also had a higher median age (43 years) than those with one or two abnormalities (39 years, p = 0.005) (Additional file 1).Patients with CK (WHO/ICC) had the highest median age (48 years, p < 0.001).
The number of patients progressively increased upto the fifth decade (68%) and declined subsequently (13% above 60 years) (Fig. 1A).The age distributions of normal and abnormal karyotypes were similar to the overall distribution, even when the latter was categorised into subgroups.However, there were differences in the age at which each category was most common.Normal karyotypes peaked a decade later (40-59 years) than abnormal karyotypes (Fig. 1A).Karyotypes with ≥ 3 abnormalities   2, 3, 4)

Categorisation into cytogenetic risk groups:
There were 459 (25.6%) patients whose karyotypes were in the favourable risk group and 374 (21%) in the unfavourable risk group which comprised 96 (

Comparison of age distribution (Tables 5, 6, 7)
The median age of our patients was lower than in the West (42 vs 52-66 years) as shown in Table 5 even when similar age groups were compared (39 vs 44 years in those ≤ 59 years as reported by Grimwade et al.) [9, 10, 13-15, 17, 18].It was also lower than in one study from Japan (mean age 51.4 years) but comparable to another, as well as the rest of Asia and N. Africa (37-48 years) [11,17,[19][20][21][22][23][24][25][26][27][28].The lower age in most of Asia and N. Africa (Tables 6 and 7 respectively) could be due to geographic and/or ethnic differences in the response to environmental factors that predispose to the development of leukemia.
Trisomy 8 was most common in the age group 40-49 years and abnormalities of chromosomes 5 and 7 (high-risk abnormalities) at 50-59 years, one to two decades earlier than in the West (60-> 80 years) [16,35].The age distribution of these abnormalities which were relatively uncommon in most of S.E.Asia were similar to our study [11,21,25].Deletions are thought to be more common in older individuals because they are considered to be a result of cumulative DNA damage [1,35] (Fig. 3).5, 6 7 & Fig. 4)
A comparison of the frequencies of our common abnormalities with the literature is shown in Additional files 6-8 and Fig. 4. The t (15;17), our most common abnormality (16.7%), had a higher frequency (p < 0.001) than in the West (9.6%) and N. Africa (7.7%) and S.E.Asia (13.1%) [10,11,13,14,[16][17][18][20][21][22][23][24][25][26][27][28].Its frequency was low (< 4%) in Morocco and Malaysia, where it was not the most common abnormality [24,27].The higher frequency of the t(15;17) in most of S.E Asia (11-17% in all but one study) compared to the West could be related to the younger age at presentation, as well as genetic and ethnic factors that predispose individuals to breakage of the PML gene [22,38].The high frequency in our study could also be because ours is a referral centre for acute promyelocytic leukemia having initiated arsenic trioxide treatment very early in India.The t(15;17) can be overlooked in karyotypes with suboptimal morphology.FISH analysis was done in most of our patients with/suspected to have acute promyelocytic leukemia, for confirmation, and to establish baseline values for assessment of cytogenetic response post treatment.
The t(8;21) was the most common abnormality in all three other reports from South Asia (8.3-20.8%)[29][30][31] The t(8;21) and the inv(16) were twice as common (14.7% and 4% respectively, p < 0.001) as in our patients in the large study from India (1906 patients) [30].These differences could be due to the reasons mentioned above.The frequencies of t(8;21) and the inv(16)/t(16;16) were similar (21% each) in the other Indian study in which AML M2, M4 and M5 subtypes accounted for 43%,23% and 8% respectively; these unusually high frequencies which differ from all other reports could be because of referral bias, the short duration (two years) and the relatively small number (173) of patients from a single institution [31].
We had more patients with monosomy 17/del 17p than in China (p < 0.001) and Egypt (p = 0.03) [21,28].Trisomy 21 was more common (p < 0.001) than in the West and S.E.Asia; it was not reported from N. Africa [9-12, 18, 21, 22].The higher frequency of high-risk abnormalities in our study as compared to S.E Asia could be due to the interplay of environmental factors and ethnic differences because abnormalities such as the t(15;17) have frequencies more similar to our findings than the West.
To summarise, our data confirms the lower (one to two decades) median age of patients (~ 42 years) with AML in Asia and Africa compared to Western countries.While the frequency of our abnormal karyotypes is comparable to the literature, there are similarities and differences with respect to the common abnormalities.We had more patients with the t(8;21) than in the West, but fewer than in the rest of Asia and Africa.Other major differences included higher frequencies of the t(15;17), trisomy 8 and trisomy 21, and a lower frequency of the inv (16).The high-risk abnormalities such as monosomy 7 and del 5q/monosomy 5 were also more common than in other regions while the inv(3)/t(3;3) and monosomy 17/del 17p had higher frequencies than in S.E.Asia and N. Africa; these abnormalities were more common in younger patients (≤ 60 years) compared to the West.A limitation of this report is the lack of molecular profile of these patients who were evaluated over a long period of time when such assessment was not always feasible.These differences in the median age and frequency of AML-associated cytogenetic abnormalities in different parts of the world could reflect ethnic/genetic differences in the susceptibility to environmental agents associated with leukemogenesis and the response to genetic damage.More detailed epidemiological studies of possible environmental exposure coupled with next-generation sequencing and emerging technologies such as optical genome mapping to look for germline abnormalities that could predispose to these conditions would help to better understand why some chromosomal abnormalities are more common than others in different geographic regions and ethnic groups.

Fig. 1
Fig. 1 Age distribution: A. All patients, normal and abnormal karyotypes.B. One, two and three or more abnormalities, complex karyotypes and monosomal karyotypes.C. Abnormalities as per Moorman classification.D. Types of abnormalities/subtypes .

Fig. 2
Fig. 2 Age distribution of A. Common RGA.B. Common MRC and other abnormalities

Fig. 4
Fig. 4 Comparison of weighted averages: A. Normal and abnormal karyotypes.B. Common RGA and complex karyotypes C. Other RGA.D. Common MRC and other abnormalities

Table 1
Overview of 1791 adult patients with AML ≥ 3 abnormalities in the absence of RGA ; ***, ELN definition: ≥ 3 abnormalities in the absence of RGA and hyperdiploid karyotypes without structural abnormalities; ^ , abnormalities other than RGA or MRC * to indicate that normal karyotypes comprise AML-NOS; **WHO/ICC definition:

Table 6
Comparison of findings with reports from South-East Asia

Table 7
Comparison of findings with reports from North Africa & South Asia