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This is the published version of a paper published in American Journal of Industrial Medicine.
Citation for the original published paper (version of record):
Forsell, K., Björ, O., Järvholm, B., Nilsson, R., Andersson, E. (2020)
Hematologic malignancy in tanker crewmembers: a case#referent study among male Swedish seafarers
American Journal of Industrial Medicine, 63(8): 685-692 https://doi.org/10.1002/ajim.23122
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Am J Ind Med. 2020;63:685–692. wileyonlinelibrary.com/journal/ajim
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685R E S E A R C H A R T I C L E
Hematologic malignancy in tanker crewmembers:
A case ‐referent study among male Swedish seafarers
Karl Forsell MD, PhD
1| Ove Björ PhD
2| Bengt Järvholm MD
3| Ralph Nilsson MD, PhD
1| Eva Andersson MD
11Department of Occupational and Environmental Medicine, Sahlgrenska Academy, Gothenburg University, Gothenburg, Sweden
2Department of Radiation Science, Oncology, Umeå University, Umeå, Sweden
3Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden
Correspondence
Karl Forsell, Arbets‐och Miljömedicin, Norrlands Universitetssjukhus, 901 85 Umeå, Sweden.
Email:karl.forsell@amm.gu.se
Funding information the Swedish AFA Insurance, Grant/Award Number: 100085
Abstract
Background: Work on Swedish petroleum tankers before the late 1980s has been associated with an increased risk of hematologic malignancy (HM). Since then, ship modernizations have decreased occupational exposure to gases, including the car- cinogen benzene. We explored the risk of HMs in Swedish seafarers who had worked on newer types of tankers.
Methods: A case ‐referent study in male seafarers from a cohort of all Swedish seafarers was set up by record linkage with the Swedish Cancer Registry using the subjects' personal identification number. For each case (N = 315), five referents were randomly chosen from within the cohort, matched by birth year and three different periods of first sea service (<1985, 1985 ‐1991, and ≥1992). Information on the type of ship and dates of service was retrieved from the Swedish Seafarers' Registry. Odds ratios (OR) were calculated by conditional logistic regression together with 95% confidence intervals (CI).
Results: The OR of HM was 1.07 (95% CI, 0.80 ‐1.42) for work on tankers. In seafarers that had started to work on tankers ≥1985, the OR was 0.85 (95% CI, 0.50‐1.43). For those who started to work on tankers before 1985, the OR was 1.17 (95% CI, 0.84 ‐ 1.21) and 1.32 (95% CI, 0.86 ‐2.03) if the cumulative time on tankers exceeded 5 years of service. In this last group, the OR of multiple myeloma was 5.39 (95% CI, 1.11 ‐26.1).
Conclusion: Although limited by crude exposure contrast and a short follow ‐up, work on tankers after 1985 was not associated with an increased risk of HM among Swedish seafarers.
K E Y W O R D S
benzene, leukemia, lymphoma, multiple myeloma, tanker
1 | I N T R O D U C T I O N
On board tankers, benzene can be a constituent of the petroleum cargo or transported as a main product on chemical tankers. Crew- members can be exposed to benzene during loading and unloading cargo holds or during the different maintenance tasks involved.
While open or manual systems were common for such work in the past, potentially exposing a deck crewmember to high benzene levels (eg,“gauging” by inspecting the cargo level through a vault), the in- troduction of closed systems have decreased occupational benzene exposures.1‐8 Closed systems were introduced on Swedish tankers during the 1980s. According to interviews with seafarers and
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inspectors, there were some problems with their functionality in the first years but most systems worked well 5 to 10 years later.
Occupational exposure to benzene is associated with leukopenia, agranulocytosis, pancytopenia, and myelodysplastic syndrome.9,10 Benzene has also been associated with an increased risk of hematologic malignancies (HMs): The International Agency for Research on Cancer (IARC) classifies benzene as an established risk factor of acute myeloid leukemia (AML) and acute non‐lymphocytic leukemia (ANLL) (acute monocytic leukemia, acute erythroid leukemia, and AML) and a suspected risk factor of acute (ALL) and chronic lymphocytic leukemia (CLL), non‐ Hodgkin's lymphoma (NHL), and multiple myeloma (MM).10,11
It is not the benzene molecule in itself that induces molecular da- mage and cancer. These effects are attributed to certain benzene‐ metabolites, such as hydroquinone and trans,trans‐myconaldehyde, and the formation of reactive oxygen species.12‐15The pattern of exposure appears to be important as well: important cumulative exposures and less cumulative but with repeated high/peak exposures are both exposure patterns associated with an increased risk of HMs.13,16‐18
Epidemiological studies have shown increased risks of HMs for tanker crewmembers. Nilsson et al19 found an increased risk of leukemia in Swedish seafarers having worked on product or chemical tankers between 1971 and 1987 (odds ratio [OR], 2.6; 95% con- fidence interval [CI], 1.1‐5.9). Saarni et al20also found an increased risk of leukemia in Finnish seafarers who had worked on deck tankers between 1967 and 1992 (OR, 2.06; 95% CI, 1.01‐5.06). A study on cancer incidence in Danish seafarers found no increased risk of HM in a subgroup of seafarers who had had their longest duration of employment on tankers.21However, there were only seven cases of HM, and the duration of employment on tankers was not reported.
Our objective was to study the risk of HM among Swedish sea- farers in relation to start of employment on more modern types of tankers. Another objective was to study the risk of HM in relation to the length of tanker employment.
2 | M E T H O D S
2.1 | Study design and subjects
The study was a nested case‐referent study within a cohort of all Swedish seafarers born in 1920 or later and with at least one re- gistered sea service in the digital Swedish Seafarers' Registry (SR) between 1 January 1985 and 31 December 2014. The SR is held by the governmental Swedish Transport Agency. Only male cases and referents were selected from the cohort sincefew women had served on tankers. The SR was digitized in 1985 but included also any sea service that had occurred before 1985. Accordingly, all seafarers had at least one sea service registered at or after 1985 (the year of digitization of the SR), but the range of possible dates for all sea services was 1940 to 2014. There were in total 105 098 seafarers in the SR. We excluded short‐term workers (≤30 days cumulated sea service; n = 7223) before the selection of cases and referents.
Cases with HMs were identified by linkage between the cohort and the national Swedish Cancer Registry. For linkage, we used the unique personal identity number. A case was defined as a seafarer that after his first registered sea service in the SR had a diagnosis of an HM between 1985 and 2014 and was between 20 to 85 years of age at the time of diagnosis. To each case, five referents were selected at random from the seafarers in the cohort at risk at the time of diagnosis of the case (ie, incidence density sampling based on calendar time as timescale). Cases and referents were matched by birth year (+/−1 year) and first year of sea service with respect to the following three different periods: before 1985, between 1985 and 1992, and after 1992. Matching by birth year was done to allow for efficient control of age at diagnosis and generation‐ specific variability such as smoking habits. Matching by calendar period of first registered sea service was done to allow control of unmeasured changes in work environmental factors for tanker crewmembers.
In total, there were 346 male cases of HMs in the cohort. Of these, 16 individuals had had more than one HM, but only the first diagnosis was then used. Fifteen individuals were excluded since they had had a diagnosis of HM before 1985. Finally, the number of cases in the study was 315, matched with 1575 referents.
2.2 | Exposure
The SR includes information on dates for each sea service, the position held by the seafarer, the name of the ship served upon and the ship type with any eventual subcategory (eg, tanker/chemical tanker). For sea services before 1985, the SR lacked information on the ship type (only the ship's name was registered). To identify the type, we then looked for the occurrence of the same ship's name in later SR‐registrations (where type would be registered) or its occurrence in a list on tankers active before 1985 delivered to us by the Swedish Transport Agency. We also consulted websites held by laymen dedicated to the last century's Swedish maritime fleet. Since a ship's name can be reused but for dif- ferent ship types, we had to compare the information from these dif- ferent sources. The process of assigning ship type to a ship name and thus a given sea service before 1985 was done in a blinded way.
Exposure was defined as work on either a chemical tanker, a product tanker, or a crude oil tanker, henceforth indicated as“work on tankers.” The definition of a specific type of tanker was not stated in the SR. However, in Sweden, a chemical tanker is generally considered a ship with possible simultaneous carriage of different types of che- micals where each tank has its own load/discharge system and with separate pumps and piping systems. A product tanker is a vessel that transports petroleum‐based products, for example, petrol, kerosene, often with one common system for tank loading and unloading, whereas a crude oil tanker transports unrefined oil. We have no rea- son to suspect that these definitions were not applied when re- gistering a sea service in the SR. Work on tankers that transported vegetable oils, wine products, or work on gas tankers or on any other ship type than a tanker was classified as“non‐exposure.” Quantifica- tion of exposure consisted in cumulating the number of days for all tanker services together. The cumulative time was further classified
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FORSELLET AL.into two categories corresponding to a date of first tanker employ- ment before or after 1 January 1985.
2.3 | Statistical methods
The case‐referent study was matched by birth year and the period of first sea service and ORs were calculated with 95% CI with condi- tional logistic regression conditioned by the sets using the PROC LOGISTIC command in SAS 9.4. Models were adjusted for age at first sea service and, for exposed, age at first tanker service. For subgroup analyses, matched sets were maintained. The ORs of any HM for the referents were 1.0 and should be seen as reflecting the risk asso- ciated with the background exposure.
To assess latency, the results were divided by follow‐up time based on three categories: up to 15 years, 15 to 19 years, and 20 years or more from the first date of a tanker service (the first category could not be divided further due to few cases). ORs in relation to time passed since last exposure (ie, the end‐date of last tanker service) were investigated by 5‐year intervals.
The project was approved by the Regional Ethical Board.
3 | R E S U L T S
The mean age at diagnosis of cases was 58 (range 21‐85) years. For cases having started to work as seafarers before 1985, the mean age at diagnosis was 63 (36‐85) years, compared with 49 (21‐79) years for a work start≥1985. Age at first tanker service was similar for cases and referents (Table1). Fifty‐six percent of cases and 54%
of referents had worked on tankers, with a mean cumulated time of tanker service equivalent to 3.45 years and 3.42 years, respectively.
There was no statistically significant positive association be- tween work on tankers (ie, at least once) and HM (Table2). This was also true when analyzing for lymphoma and leukemia sepa- rately. An association was indicated between work on tankers and MM (OR, 2.33; 95% CI, 0.77‐7.03) (tanker service or no such service amongst myeloma cases and their referents are described in TableA1).
3.1 | First sea service on tankers after 1985
There were 20 cases of HM amongst seafarers who had had their first tanker service ≥1985 (Table 2). In this group, there was no association between work on tankers and HM, nor, with any HM‐ subtype. All ORs were below 1.0, although without statistical sig- nificance. Since cases were relatively few and their total time on tankers short (median 0.26 years compared with 2.00 for first tanker service <1985), we could not analyze the effect of cumulated tanker time in this group.
3.2 | First sea service on tankers before 1985
There were 155 cases of HM among seafarers who had started to work on tankers before 1985 (Table2). There was no statistically significant association between work on tankers and HM or any subtype. However, most ORs were increased and especially among the leukemia subtypes. Five years or more of work on tankers was significantly associated with MM, although the risk estimate was imprecise (OR, 5.39; 95% CI, 1.11‐26.1) (Table3).
The risk of HM was increased at 15 to 19 years of latency (OR, 1.93; 95% CI, 1.01‐3.68), mainly due to an increased risk of leukemia (OR, 3.10; 95% CI, 1.17‐8.22) (TableA2). The OR of CLL peaked at 16 to 20 years after exposure had ended (OR, 5.70; 95% CI, 1.26‐25.7) (TableA3).
4 | D I S C U S S I O N
The present study found no association between work on tankers
≥1985 and HM. Rather, our findings suggest a decreased risk of HM for tanker crewmembers with the transition from older types of tankers to a modernized fleet. This interpretation needs to be cau- tioned since we used a crude exposure contrast between cases and referents, and since both time of exposure and time of follow‐up were limited for tanker work≥1985. The cumulative time served on tankers seemed important, since the risk of HM appeared to be particularly increased for seafarers that had started to work on older types of tankers in combination with several years of tanker work.
Reduced occupational exposures to benzene for deck crew- members on tankers have been reported with the introduction of more closed and automatic handling of the cargo and the main- tenance of the tanks, which would have started around the end of the 1980s.1,7Typical manual operations on older tankers would involve visual inspections of cargo levels through open hatches (eg, sounding, topping, or stripping) and manual maintenance work, such as entering unloaded tanks for manual elimination of any residual cargo (ie, tank cleaning). In a review article on benzene air sampling data from marine transports of petroleum and other benzene‐containing pro- ducts during 1975 to 2000, Williams et al7 found personal time‐ weighted averages of occupational benzene exposures between 2 and 10 ppm (6.5 to 32.5 mg/m3) for open loading operations and 0.2‐ 2.0 ppm (0.7‐6.5 mg/m3) for closed loading operations. Shorter ex- posures during open operations were reported to sometimes exceed 100 ppm (325 mg/m3). The European Occupational Exposure Limit (OEL) is currently 1 ppm, equivalent to 3.25 mg/m3, which is also a recommended OEL in international seafaring by the International Maritime Organization.22 It should be noted that the use of re- spiratory protection during benzene exposure tasks was probably seldom applied by deck crewmembers even as late as into the mid‐ 1990s.1,23Furthermore, by the end of 1998, the benzene content in gasoline, a common cargo on tankers, dropped due to a decreased allowance limit from 5% v/v (volume/volume percent) to 1% v/v.24
TABLE1Selectedcharacteristicsinacase‐referentstudyonmaleseafarersfromacohortofallSwedishseafarers(1985‐2014),dividedbyfirstseaserviceforanyshiptypeandfirstservice onatankerbeforeandafter1985,respectively AnyshiptypeTankers TotalPre‐85Post‐85TotalPre‐85Post‐85 Cases NumberofindividualsN31521410117515520 Ageatstartofemployment,yAM(range)27(15‐69)23(15‐56)35(16‐69)27(15‐63)27(15‐56)28(16‐63) Seaservices,yAM(range)10.7(0.09‐38.6)14.4(0.21‐38.6)3.06(0.09‐19.7)3.45(0.01‐21.3)3.82(0.01‐21.3)0.56(0.08‐2.37) Median(Q1,Q3)8.76(2.46,18.1)13.9(7.53,20.7)1.79(0.42,3.37)1.74(0.47,5.59)2.00(0.59,5.85)0.26(0.10,0.66) Referents NumberofindividualsN15751070505856739117 Ageatstartofanyemployment,yAM(range)27(14‐73)23(14‐62)35(16‐73)26(15‐69)25(15‐58)32(16‐69) Seaservices,yAM(range)11.6(0.08‐42.3)15.7(0.09‐42.3)2.94(0.08‐24.7)3.43(0.01‐28.7)3.78(0.01‐28.7)1.21(0.01‐14.9) Median(Q1,Q3)10.1(2.46,18.7)15.4(8.53,21.5)1.37(0.40,3.89)1.68(0.56,4.72)2.06(0.74,5.39)0.42(0.17,1.46) Note:Thearithmeticmean(AM)withrangeandmedianwithfirstandthirdquartiles(Q1,Q3)aredisplayedforseaservicesonanyshiptypeandfortankersspecifically.
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FORSELLET AL.The suggested reduced risk of HM in our study after the introduction of modern tankers complies with a register‐based study on cancer incidence in a cohort of Danish seafarers.21 The authors found no increase of HM among seafarers who had most of their employment time (≥50%) on tankers, although the number of HM‐cases was limited (N = 7). In the cohort, work at sea had occurred between 1986 and 1999, which roughly corresponds to our second studied period of 1985 to 2014. In a recent follow‐up using the same cohort, Ugelvig Petersen et al25again found no increased risk of HM. That article does not report specifically on HM among tanker crewmembers, other than mentioning an increased incidence of Hodgkin's lymphoma (HL) among males. The result was
interpreted as a finding by chance since benzene is not associated with HL.
The OR for MM was significantly increased for seafarers with a start on tankers before 1985 and who had continued to work on tankers for≥5 years. In its summary on benzene and cancer in 2012, IARC described a positive association between benzene exposure and MM.10Our findings are thus in line with the IARC's assessment.
In a previous case‐referent study among Swedish seafarers be- tween 1971 and 1987, the OR of NHL was 3.3 (95% CI, 1.1‐10.6) for work on product or chemical tankers.19In our study, the OR was 1.22 (tanker service≥5 years, start <1985), although this result was not T A B L E 2 Cases and odds ratios (OR) with 95% confidence intervals (95% CI) of hematologic malignancy for tanker crewmembers in a case‐
referent study on male seafarers from a cohort of all Swedish seafarers (1985‐2014)
Tankers Tanker pre‐85 Tanker post‐85
ICD Total cases Cases OR (95% CI) Cases OR (95% CI) Cases OR (95% CI)
Lymphoma 200‐203 194 104 1.06 (0.73‐1.53) 91 1.15 (0.74‐1.79) 13 0.87 (0.45‐1.66)
NHL 200, 202 138 72 0.91 (0.60‐1.40) 63 0.93 (0.57‐1.52) 9 0.86 (0.40‐1.86)
Hodgkin's 201 21 8 1.12 (0.37‐3.36) 5 2.15 (0.23‐20.3) 3 0.84 (0.21‐3.40)
Myeloma 203 35 24 2.33 (0.77‐7.03) 23 3.09 (0.82‐11.6) 1
Leukemia 204‐209 121 71 1.07 (0.68‐1.67) 64 1.17 (0.70‐1.93) 7 0.81 (0.34‐1.95)
CLL 204.1 31 19 1.39 (0.56‐3.45) 18 1.38 (0.53‐3.65) 1
AML 205.0 10 4 0.35 (0.06‐1.95) 4 0.95 (0.08‐11.1) 0
Myeloic 205.0, 205.1, 205.9 43 25 0.86 (0.41‐1.81) 25 1.34 (0.55‐3.29) 0 ANLL 205.0, 206.0, 207.2 17 10 0.74 (0.22‐2.57) 10 1.75 (0.30‐10.1) 0
Any hematologic 200‐209 315 175 1.07 (0.80‐1.42) 155 1.17 (0.84‐1.62) 20 0.85 (0.50‐1.43) Note: For all estimates, the comparison group is workers who never worked on a tanker (OR of 1.00).
Abbreviations: AML, acute myeloid leukemia; ANLL, acute nonlymphocytic leukemia; CI, confidence interval; CLL, chronic lymphocytic leukemia; ICD, International Classification of Diseases; NHL, non‐Hodgkin's lymphoma; OR, odds ratio.
T A B L E 3 Cases and odds ratios (OR) with 95% confidence intervals (95% CI) of hematologic malignancy among tanker crewmembers having worked before 1985 with respect to more than 5 years' cumulated time on tankers or less, in a case‐referent study on male seafarers from a cohort of all Swedish seafarers (1985‐2014)
Tanker pre‐85 and >5 y Tanker pre‐85 and <5 y
ICD Cases OR (95% CI) Cases OR (95% CI)
Lymphoma 200‐203 30 1.48 (0.84‐2.60) 61 1.06 (0.67‐1.68)
NHL 200, 202 23 1.22 (0.65‐2.28) 40 0.84 (0.50‐1.42)
Hodgkin 201 0 5 2.74 (0.29‐26.0)
Myeloma 203 7 5.39 (1.11‐26.1) 16 2.70 (0.70‐10.4)
Leukemia 204‐209 17 1.11 (0.57‐2.18) 47 1.19 (0.70‐2.02)
CLL 204.1 7 1.62 (0.50‐5.28) 11 1.27 (0.45‐3.61)
AML 205.0 2 2
Myeloic 205.0, 205.1, 205.9 5 0.91 (0.27‐3.05) 20 1.53 (0.61‐3.83)
ANLL 205.0, 206.0, 207.2 4 4.51 (0.51‐39.7) 6 1.29 (0.20‐8.44)
Any hematologic 200‐209 47 1.32 (0.86‐2.03) 108 1.11 (0.79‐1.58)
Note: For all estimates, the comparison group is workers who never worked on a tanker (OR of 1.00).
Abbreviations: AML, acute myeloid leukemia; ANLL, acute nonlymphocytic leukemia; CI, confidence interval; CLL, chronic lymphocytic leukemia; ICD, International Classification of Diseases; NHL, non‐Hodgkin's lymphoma; OR, odds ratio.
statistically significant. As with MM, associations between NHL and previous occupational benzene exposure have been found in several studies, although the associations appear weaker than for MM.10,13
The main strength of the present study was the detailed in- formation on service times and types of ships for all sea services.
Other studies on cancer among seafarers often rely on rather crude information on occupational settings (ie,“seafarer” as only informa- tion given, or“last reported sea service”). We also had high‐quality data on cancer from the Swedish CR.26Furthermore, using referents from the same population of Swedish seafarers reduced the chance of results biased by differences in lifestyle factors (eg, smoking).
One important limitation was that we had few exposed cases for tanker work≥1985, which rendered wide CI for this calendar period.
Another limitation was few exposed cases with AML (n = 4), the most convincing causal effect from benzene exposures.
In the cohort, roughly 20% of seafarers had served on tankers.
However, in the case‐referent study, around 55% of both cases and referents had worked on tankers. Among seafarers who started be- fore 1985, 75% of cases and 71% of referents had worked on tan- kers. Hence, exposure turned out to be very common in the group of seafarers with the longest time of observation. That became a weakness of the study. Furthermore, the exposure duration, in terms of cumulated time on board tankers, was much shorter among sea- farers who had started≥1985 than those who had started before 1985 (Table 1). This can probably be explained by the fact that seafarers who had started out on the seas before 1985 had, in general, a much longer cumulated time of service, and thus the chance of at some time or another having worked on a tanker was higher among them. This fact, in combination with a shorter follow‐up for HM, weakened our possibilities to detect any increased risk in this group. Type of cargo was not noted in the SR, and also other possible sources for benzene exposures while serving on other ships than tankers were not known.
Work on tankers was not confined to a particular group of seafarers. In fact, only 5% of seafarers on tankers had not worked on other types of ships, which all others (95%) had done. Furthermore, we had no information on other occupations held by each individual seafarer, either before, during, or after their seafaring career. The contribution of benzene exposures from other occupations might have been important, since the mean cumulated sea service time turned out to be 11 years, which only corresponds to half a working life (time off duty as a seafarer included).
The SR did not include seafarers having ended as such before 1985, that is, the year of digitization of the SR. Thus, we ignored any case of HM in this group of seafarers. If seafarers with a diagnosis of HM from work on tankers would have stopped working before 1985 to a higher extent than their colleagues during the same period, this might have led to a healthy‐worker effect (HWE). However, we believe such an HWE would be small, since HMs are rare malignancies.
In summary, the main limitation with our study was a poor ex- posure contrast between cases and referents, that is, tanker work was common in both groups. The contrast could perhaps be
heightened with a more precise exposure assessment. For instance, a Job Exposure Matrix might be useful, including even other variables such as position on board, type of cargo transported, and the ship's trade. We are currently investigating such a possibility in a larger study sample by pooling data on seafarers from all the Nordic countries.
5 | C O N C L U S I O N S
In the present study, work on petroleum tankers≥1985 was not associated with an increased risk of HM. However, this apparent lack of an association should be corroborated by further studies on sea- farers with more cumulative time on tankers for this later period, and with a longer follow‐up. The findings suggest an increased risk of HM among seafarers who had worked on tankers before 1985, specifi- cally for those with≥5 years of tanker service.
A C K N O W L E D G M E N T S
This work was performed at the Department of Occupational and Environmental Medicine, Sahlgrenska Academy, Gothenburg Uni- versity, Sweden. This project was funded by the Swedish AFA In- surance (D‐nr 100085). We would sincerely like to thank Senior Officer Johan Bagge, at the Swedish Maritime Administration, and Linda Eriksson at SITS/Swedish Transport Agency, Klubb Maritim‐ Göteborg (Swedish Shipping Historical Society– Gothenburg), SAN (The Swedish Maritime Joint Work Environment Council), and all enthusiasts behind websites with information on historic or modern ships.
C O N F L I C T S O F I N T E R E S T
The authors declare that there are no conflicts of interest.
A U T H O R C O N T R I B U T I O N S
RN was the founder of the cohort, from which the cases and re- ferents were retrieved. He also applied for and received the funding mentioned in the study. RN, EA, and BJ, together with KF (a PhD‐ student at the time) developed the project with a case‐referent study and a project description. The statistician OB contributed in parti- cular to the use of incidence density sampling (the matching) and organized the framework for OR‐analyses. KF and EA did the ex- posure assessments, which included retrieving information on ship types where this was not known, and classing cases and referents (blinded) exposed or not exposed, and made OR‐analyses irrespec- tive of each other, that is, on their own, to compare that results were identical. KF authored the study and all of its contents, including the tables. The conclusions from the results were made together by all authors. Finally, EA granted the article's submission.
E T H I C S S T A T E M E N T
The project was approved by the Regional Ethical Board of Go- thenburg (193‐13). Since the study was a register‐based study on many individuals and spanning a longer period of time, individually
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FORSELLET AL.informed consent was not considered feasible. However, updated information on the study has been offered publicly through media interviews within the trade and through our own website (www.
maritimehealth.gu.se).
O R C I D
Karl Forsell http://orcid.org/0000-0002-4625-2401
R E F E R E N C E S
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How to cite this article: Forsell K, Björ O, Järvholm B, Nilsson R, Andersson E. Hematologic malignancy in tanker
crewmembers: A case‐referent study among male Swedish seafarers. Am J Ind Med. 2020;63:685–692.
https://doi.org/10.1002/ajim.23122
A P P E N D I X See TablesA1‐A3.
T A B L E A2 Latency of hematologic malignancy (HM) for seafarers that had worked on tankers within a case‐referent study on male seafarers from a cohort of all Swedish seafarers (1985‐2014)
Cases OR 95% CI
HM
15 y or less 11 0.60 0.31‐1.17
15 to 19 y 15 1.93 1.01‐3.68
20 y or more 149 1.12 0.81‐1.54
Leukemia
15 y or less 3 0.47 0.13‐1.62
15 to 19 y 8 3.10 1.17‐8.22
20 y or more 60 1.05 0.64‐1.72
Lymphoma
15 y or less 8 0.68 0.31‐1.49
15 to 19 y 7 1.35 0.55‐3.29
20 y or more 89 1.17 0.77‐1.78
Note: Odds ratio (OR) with 95% confidence interval (95% CI) for HM and subtypes with three different categories of cumulated time on tankers compared to no tanker service.
T A B L E A1 Cases of multiple myeloma (MM) with referents and tanker or no tanker service within a case‐referent study on male seafarers from a cohort of all Swedish seafarers (1985‐2014)
Tanker No tanker Total
Total
MM 24 11 35
Referents 101 74 175
Total 125 85 210
Pre‐85
MM 23 3 26
Referents 98 32 130
Total 121 35 156
Post‐85
MM 1 8 9
Referents 3 42 45
Total 4 50 54
T A B L E A3 Time since last exposure and hematologic malignancy (HM) for seafarers that had worked on tankers within a case‐referent study on male seafarers from a cohort of all Swedish seafarers (1985‐2014)
Interval Cases OR 95% CI
HM
≤5 y 25 0.85 0.52‐1.38
6‐10 y 24 1.46 0.88‐2.42
11‐15 y 22 1.20 0.72‐2.02
16‐20 y 22 1.18 0.70‐1.99
>20 y 82 0.99 0.70‐1.41
Lymphoma
≤5 y 17 0.98 0.54‐1.79
6‐10 y 12 1.14 0.57‐2.27
11‐15 y 14 1.33 0.69‐2.58
16‐20 y 10 0.85 0.40‐1.79
>20 y 51 1.07 0.68‐1.69
NHL
≤5 y 11 0.86 0.41‐1.79
6‐10 y 10 1.07 0.50‐2.30
11‐15 y 11 1.28 0.61‐2.70
16‐20 y 7 0.70 0.29‐1.68
>20 y 33 0.88 0.52‐1.49
Leukemia
≤5 y 8 0.68 0.30‐1.54
6‐10 y 12 2.00 0.94‐4.28
11‐15 y 8 1.02 0.45‐2.32
16‐20 y 12 1.68 0.80‐3.51
>20 y 31 0.89 0.51‐1.55
CLL
≤5 y 1 0.71 0.08‐6.17
6‐10 y 3 2.78 0.54‐14.3
11‐15 y 3 2.02 0.45‐9.10
16‐20 y 5 5.70 1.26‐25.7
>20 y 7 0.81 0.27‐2.41
Note: Odds ratio (OR) with 95% confidence interval (95% CI) for HM and subtypes with five different categories of time compared to no tanker service.
Abbreviations: CLL, chronic lymphocytic leukemia; NHL, non‐Hodgkin's lymphoma.
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