Cancer mortality and survival after cancer diagnosis by migration background and socioeconomic position in Sweden

Abstract

Aims: The overall aim of this thesis was to investigate the risk of cancer mortality and survival after cancer diagnosis based on migration background and socioeconomic position in Sweden. We studied the effects of country of birth and level of education, as a proxy for socioeconomic position, on mortality due to all-site cancer (and some common specific cancers), trends in overall survival after cancer diagnosis (all sites and selected cancer sites), and all-cause and excess mortality in breast cancer patients by stage at diagnosis.

Materials and methods: The data used in this thesis are from a nationwide dataset, the Migration and Health Cohort, which was specifically designed to address health status among immigrants and among socially and economically deprived population in Sweden. In this cohort, information was retrieved through linkage between several national Swedish registers (Studies I–III). Based on country of birth, we followed individuals from the total population in the years 1961–2009 (Study I), cancer patients 45 years of age and older in the years 1961–2009 (Study II), and breast cancer patients by stage at diagnosis in the years 2004–2009 (Study III). The outcomes were cancer mortality (Study I) and survival (Studies II and III). We calculated mortality rate ratios (MRRs) (Study I), age-standardized rates (ASRs) (Study I), hazard ratios (HRs) (Studies II and III), relative risk ratios (RRRs), and relative excess rate (RER) (Study III) with 95% confidence intervals (CIs) using Poisson (for MRR and RER), Cox, and multinomial logistic regression models, respectively.

Results: We observed a downward trend in all-site ASRs over the past two decades in men but no change in women regardless of country of birth (Study I). In comparison with Sweden-born men, all-site cancer mortality was slightly higher in foreign-born men, with men born in Angola, Laos, and Cambodia having the highest risk. Among women, a similar risk was observed in foreign-born and Sweden-born individuals (Study I). However, the findings varied across different cancer sites; foreign-born individuals had lower risks of colon, prostate, and breast cancer mortality but higher risks of lung and cervical cancer mortality compared with Sweden-born individuals (Study I). All-site cancer mortality increased with decreasing level of education (Study I). A similar pattern of level of education was observed with regard to all-cause mortality in breast cancer patients (Study III). Overall, after the year 2000, overall survival was lower in foreign-born cancer patients, who were on average 4 years younger at the time of diagnosis, compared with cancer patients born in Sweden (Study II). The results were almost the same independent of sex, duration of residence, and age at diagnosis. The overall survival trends for prostate and breast cancers were also similar to the trend for all-site cancers (Study II). Not surprisingly, survival decreased with increasing tumor size, number of lymph nodes involved, presence of metastasis, comorbidity, and anatomic stage in breast cancer patients, particularly among foreign-born patients (Study III). We observed a higher risk of stage II tumor (stage I as baseline) among all foreign-born breast cancer patients and patients born in Asia compared with those born in Sweden (Study III). In addition, a poorer survival was observed among all foreign-born breast cancer patients with stages III–IV cancer and also patients born in Asia and Southern Europe with stages III and IV cancer, respectively, compared with breast cancer patients born in Sweden (Study III). Analyses taking into account reason for migration showed that refugee patients with breast cancer had a higher risk of both all-cause and excess mortality, compared with Sweden-born patients. In the stratified analysis by stage, the risks were prominent in advanced stages (III–IV) of disease. The higher risks of all-cause and excess mortality were not statistically significant. Furthermore, compared with non-refugee patients, we found non-significantly higher risks of both all-cause and excess mortality among refugee women with advanced-stage cancer.

Conclusions: Country of birth is an important determinant of risk of cancer mortality and survival after cancer diagnosis. Increased mortality risk with decreasing level of education, remains a major risk indicator for these events. The decreased overall survival among foreign-born patients after the year 2000 and poor prognosis among foreign-born breast cancer patients with advanced stages of the disease need further investigation to fully understand the reasons behind these disparities.