Abstract
Introduction The association between SES and survival in MM and AML has not been studied in detail and the limited results are inconclusive. In the present study the impact of SES on survival was analyzed in a large population-based cohort of MM and AML patients.
Patients and Methods From the Swedish Cancer Register we identified all individuals diagnosed with MM and AML between 1973 and 2003. We used type of occupation, combined into seven groups (blue-collar worker, farmer, lower white-collar worker, higher white-collar worker, self-employed, retired, and unknown), from the Swedish National Census Databases as a proxy for SES. The relative risk of death (any cause) in relation to type of occupation and calendar period was estimated using Cox’s proportional hazards regression adjusted for age, sex, calendar period and area of residence. We also conducted analyses stratified by calendar period (1973–1979, 1980–1989, 1990–1999, and 2000–2003).
Results A total of 14,200 and 8,831 patients were diagnosed with MM and AML, respectively. The median age at diagnosis was 71.8 years in patients with MM and 69.1 years in AML. The SES distribution was similar between the two diseases. The majority of patients were blue-collar (38.0; 39.5%) and white-collar workers (36.4; 37%), with lower white-collar workers dominating the latter group. Women had a significantly lower mortality than men both among MM (p<0.001) and AML (p<0.05) patients. The mortality among patients diagnosed in more recent calendar periods was lower than among patients diagnosed earlier (p<0.001) Overall, higher white-collar workers had a significantly lower mortality compared to blue-collar workers for both MM (p<0.001) and AML (p<0.001). No significant differences were found between the other SES groups. In MM, analyses stratified by calendar period revealed that the mortality did not differ between the SES groups in the first two calendar periods, but in the third calendar period, 1990–1999, both higher and lower white-collar workers had a significantly lower mortality compared to blue collar workers, hazard ratios (HR) 0.85 (95% CI, 0.75–0.96) and 0.91 (95% CI 0.85–0.98), respectively. In the fourth period the mortality followed the same pattern as in the third period with lower mortality among both higher [HR 0.66 (95% CI, 0.50–0.88)] and lower [HR 0.82 (95% CI, 0.69–0.96)] white-collar workers. In AML patients no difference in mortality in relation to SES was found during the first calendar period. During the last three periods, however, a lower mortality was observed in higher white-collar workers compared to blue-collar workers, HR: 0.79 (0.66–0.95), 0.79 (0.67–0.93) and 0.74 (0.57–0.96) in the periods 1980–1989, 1990–1999 and 2000–2003, respectively.
Conclusion SES, here defined as occupational profession, was significantly associated with prognosis in both MM and AML. Most conspicuously, a lower mortality was recorded in white-collar workers during more recent calendar periods. Differences in time to diagnosis (lead-time bias) and treatment strategies may be important factors contributing to this finding. Future studies may identify the relative impact of these and potentially other factors.
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