Socioeconomic inequality in cancer survival – changes over time. A population-based study, Denmark, 1987–2013

<b>Background:</b> Socioeconomic inequality in survival after cancer have been reported in several countries and also in Denmark. Changes in cancer diagnostics and treatment may have changed the gap in survival between affluent and deprived patients and we investigated if the differences in relative survival by income has changed in Danish cancer patients over the past 25 years. <b>Methods:</b> The 1- and 5-year relative survival by income quintile is computed by comparing survival among cancer patients diagnosed 1987–2009 to the survival of a cancer-free matched sample of the background population. The comparison is done within the 15 most common cancers and all cancers combined. The gap in relative survival due to socioeconomic inequality for the period 1987–1991 is compared the period 2005–2009. <b>Results:</b> The relative 5-year survival increased for all 15 cancer sites investigated in the study period. In general, low-income patients diagnosed in 1987–1991 had between 0% and 11% units lower 5-year relative survival compared with high-income patients; however, only four sites (breast, prostate, bladder and head &amp; neck) were statistically different. In patients diagnosed 2005–2009, the gap in 5-year RS was ranging from 2% to 22% units and statistically significantly different for 9 out of 15 sites. The results for 1-year relative survival were similar to the 5-year survival gap. An estimated 22% of all deaths at five years after diagnosis could be avoided had patients in all income groups had same survival as the high-income group. <b>Conclusion:</b> In this nationwide population-based study, we observed that the large improvements in both short- and long-term cancer survival among patients diagnosed 1987–2009. The improvements have been most pronounced for high-income cancer patients, leading to stable or even increasing survival differences between richest and poorest patients. Improving survival among low-income patients would improve survival rates among Danish cancer patients overall and reduce differences in survival when compared to other Western European countries.

**背景：** 多个国家均已报道癌症确诊后生存状况存在社会经济不平等现象，丹麦亦不例外。癌症诊疗技术的变革或已改变了高收入与低收入患者间的生存差距，本研究旨在探究过去25年间，丹麦癌症患者按收入划分的相对生存率（relative survival）差异是否发生了变化。
**方法：** 本研究通过将1987年至2009年确诊的癌症患者的生存情况，与背景人群中匹配的无癌对照样本的生存情况进行对比，计算按收入五分位（income quintile）分组的1年及5年相对生存率。对比分析覆盖15种最常见癌症以及所有癌症合并队列。将1987年至1991年期间因社会经济不平等导致的相对生存率差距，与2005年至2009年的对应差距进行对比。
**结果：** 本研究涉及的15种癌症部位的5年相对生存率在研究周期内均有所提升。总体而言，1987年至1991年确诊的低收入患者，其5年相对生存率较高收入患者低0至11个百分点；但仅乳腺、前列腺、膀胱及头颈部4种癌症的差异具有统计学意义。2005年至2009年确诊的患者中，5年相对生存率的差距为2至22个百分点，15种癌症中有9种的差异具有统计学意义。1年相对生存率的结果与5年生存差距的趋势一致。若所有收入组别的患者生存率均与高收入组持平，估计诊断后5年内的总死亡病例中有22%可避免。
**结论：** 本项基于全国人群的研究显示，1987年至2009年确诊的癌症患者的短期及长期癌症生存率均得到显著改善。但此类改善在高收入癌症患者中最为突出，导致贫富患者间的生存差距保持稳定甚至进一步扩大。提升低收入患者的生存率，可整体改善丹麦癌症患者的生存率水平，并缩小丹麦与其他西欧国家间的生存差异。