This was a retrospective descriptive cross-sectional chart review of all cases of primary hematopoietic cell neoplasms in bone marrow aspirates that presented during the 10-year period from January 2005 to December 2014 at SMC. Data were extracted from archived marrow biopsy reports. Demographic and laboratory data were accessed from archived records in the hospital information system. The diagnosis was based on morphology, flowcytometry and molecular analysis. Bahrain population statistics were accessed in the Bahrain open data portal.

The crude incidence rate, age-specific incidence rates and age-standardized incidence rates (ASIRs) were calculated. The crude incidence rate was calculated based on the mid-time of the total Bahraini population denominator for the period of 2005 to 2014. The age-specific incidence rate was calculated by dividing the total number of new primary hematologic malignancy cases diagnosed in the study period by the at-risk population for each age-group and multiplied by 100,000 of the population. The World Standard Population (WHO 2000 - 2025) was used for direct standardization to calculate ASIRs per 100,000 of the population. The ASIRs were calculated according to the Cancer Incidence in Five Continents series, published by the International Agency for Research on Cancer and the International Association of Cancer Registries.4

A total of 272 new primary hematologic malignancy cases were diagnosed during the 10-year period of which 161 (59.2%) were males and 111 (40.8%) were females. The median age of the study population was 42 years (95% CI 38 - 48). The median age of males and females were 39 years (95% CI 34 - 49) and 46 years (95% CI 41 - 52), respectively (Table 1). There was no statistically significant difference between the median ages of males and females in the study population. Acute myeloid leukemia (AML) was the most frequently reported hematologic malignancy in our study (26.1%), with a median age of incidence of 39 years. Acute lymphoblastic leukemia (ALL) was the second most common reported type (22.8%, median age 9 years), followed by multiple myeloma (MM) (16.2%, median age 57 years), chronic myeloid leukemia (CML) (14%, median age 39.5 years), myelodysplastic syndrome (MDS) (12.5%, median age 56 years) and chronic lymphocytic leukemia (CLL) (5.5%, median age 65 years) in reducing order of frequency (Table 1). In addition, eight cases of other chronic myeloproliferative disorders (CMPD) were reported, including primary myelofibrosis (n = 3), essential thrombocythemia (n = 3) and polycythemia vera (n = 2). Finally, two cases of hairy cell leukemia were seen: a 25-year-old female and a 42-year-old male.

The overall average crude annual incidence rate of these malignancies for the study period was 4.8/105. The corresponding rates were 5.6 in males and 3.9 in females (Table 1). Considering specific categories of primary hematologic malignancies, the crude incidence rate of AML was the highest (1.2/105). This was followed by ALL, with a crude incidence rate of 1.1/105. The crude incidence rates for MM, CML and MDS were 0.8, 0.7 and 0.6 per 100,000 of the population, respectively. CLL was observed to have the lowest crude incidence rate (0.3/105), excluding other CMPD and hairy cell leukemia. The crude incidence rates were higher in males than in females for AML, ALL and MDS, whereas the rates, as well as the male/female ratios, were approximately equivalent in CML, CLL and MM (Table 1).

The age-specific annual incidence rates per 100,000 of the population by age group for primary myeloid and lymphoid malignancies are illustrated in Figure 1a and b, respectively. The incidence of AML showed a peak at 60 to 74 years (12.8). The CML incidence rate was 4.6 at 30 to 44 years, declining at 45 to 59 years before increasing gradually, reaching 12.4 at 75+ years. The MDS rates increased sharply after the age of 59, reaching a maximum at 75+ years (20.9). The ALL was more common in childhood, with an incidence rate of 6.9 in the age group of 0 to 14 years (0 - 4 years: 3.13, 5 - 9 years: 2, 10 - 14 years: 1.72), whereas the CLL rose steeply from age 45-59 reaching a maximum at 75+ years (14.5). The age-specific incidence rates of MM rose steeply from age 30 to 44, reaching a peak at 75+ years (18.2).

Figure 1.

Age-specific incidence rates per 100,000 per year for primary myeloid (a) and primary lymphoid (b) malignancies among Bahrainis (2005 - 2014).

ALL: acute lymphocytic leukemia; AML: acute myeloid leukemia; Incidence rate: age-specific incidence rate; CLL: chronic lymphocytic leukemia; CML: chronic myeloid leukemia; MDS: myelodysplastic syndromes; MM: multiple myeloma.

(0.38MB).

The ASIRs (world) per 100,000 of the population per year of primary hematologic malignancies were calculated for males, females and both sexes to overcome the age effect and allow comparisons between different populations (Table 2). The overall ASIRs for both sexes were 1.47,1.13, 0.93, 0.85, 0.81 and 0.44 for AML, MM, ALL, MDS, CML and CLL, respectively. When incidences in males and females were compared, notable male predominance was observed in MDS and ALL with male/female ratios of 3.2 and 1.8, respectively.

The MDS were the fifth most common primary hematologic malignancy in Bahrain in our study. The male predominance of MDS was reported in most populations.4,26,27 The MDS are known to predominate in the elderly with a median age at diagnosis in the US of 76 years.27 In our study, relatively younger age groups were affected (median age at diagnosis was 56 years old), which is comparable to reports from Bangladesh (57 years) and Morocco (62 years). 6,28 The age-specific incidence rates for MDS increased with age, which is a well-known fact.26,27

The ASIR reported in our study is lower than those in the US and Germany (4.9), but more comparable to Eastern countries (e.g., Korea 1.1).19,21,26 In addition, we found that the ASIR of MDS is 3.2 times higher in males, compared to females. The male predominance was reported in the US (ASIR 1.8 times higher in males).21 The overall ASIR per 100,000 per year for MDS in our study (0.85) suggests an increasing trend, compared to the previous report in Bahrain (0.7) (Figure 2).1 Increasing trends of MDS over time were reported in the US and Europe and this might be attributed to the improved diagnosis and reporting of these malignancies. 27,29

The MM was the third most common primary hematologic malignancy in our study. The crude annual incidence rate of 0.8 per 100,000 is comparable to that in other GCC countries, but much lower than the rates reported in the (6.3) and the UK (6.3).4,7,30 We found that males and females were equally affected and this is consistent with reports in the US and Saudi Arabia.4,8 However, higher male-to-female ratios are observed in other countries, such as the UK (ratio 1.43), Morocco (ratio 1.2) and Kuwait (ratio 1.8).4,7,28

The median age at diagnosis of our patients (57 years) is similar to the data reported in Asian countries.6 A higher median age at diagnosis is reported in the West (the UK and the USA: 68 - 73 years).7,31,32 The age-specific incidence rates of MM increased with age and this is a well-known trend.28,30,31

The annual ASIR of MM in our study is 1.8 times higher than in 1991 to 1995 at the same center (1.1 versus 0.6 per 105) (Figure 2). This apparent rise in the incidence of MM is consistent with the global trend that witnessed an increase of 126% during the period of 1990 to 2016 and may be attributed to the increase in the aging population and improvement in detection rates.33 However, our ASIRs are much lower than the global rates (2.1/105 in 2016) and reported ASIRs in Western Europe, North America and Australia, but comparable to rates in North Africa, the Middle-East and Asian countries.21,33