Verdecchia A, De Angelis R, Capocaccia R, Sant M, Micheli A, Gatta G, Berrino F
Istituto Superiore di Sanità, Rome, Italy.
Int J Cancer. 1998 Jul 29;77(3):322-9. doi: 10.1002/(sici)1097-0215(19980729)77:3<322::aid-ijc2>3.0.co;2-q.
The interpretation of time trends and geographical differences of population-based survival rates is generally not easy, due to the difficulty in disentangling the effects of observational biases, diagnostic and therapeutic procedures and their interactions. Whereas descriptive analysis of relative survival is generally based on survival levels estimated at fixed time since diagnosis, interpretation issues can take advantage from the analysis of the shape of the considered relative survival. Parametric survival models allowing the estimation of the fraction of cured patients are applied here to analyze and discuss the differences in colon cancer relative survival between European countries, according to age and period of diagnosis. The survival curves of colon cancer patients are described according to 2 parameters: the proportion of cured patients and the mean survival time of fatal cases. These parameters are estimated by least square nonlinear regression of relative survival values derived from the EUROCARE Project publication. Exponential and Weibull survival functions are used to model the relative survival curve for the fraction of fatal cases. The Weibull model gives generally a better fit with respect to the exponential model, thus indicating that the mortality rate for fatal cases is decreasing with time since diagnosis. For the youngest patients, however, the 2 survival functions give practically overlapping estimates. The overall proportion of colon cancer patients in Europe that are estimated to be cured was 38.6%. This proportion increased from 36% to 40% for patients diagnosed in 1978-1980 and in 1983-1985, respectively. Accordingly, mean survival time of fatal cases increased from 1.18 to 1.52 years. According to age, the proportion of cured patients present a marked decrease from young (48.4% at age 15-44 years) to middle-aged patients (38.6% at age 5564 years) and only a mild decrease from these to the oldest patients (34.4% at age 75 or more). The opposite effect was shown by survival time of fatal cases, i.e., 1.71, 1.75 and 0.77 years for the same age classes, respectively. Proportion of cured cases and mean survival time of fatal cases tended to be positively correlated with each other across countries. Our results are consistent with the hypothesis that a real improvement in colon cancer survival took place in Europe during the years 1978-1985 and also suggest that the well-known decrease of relative survival with age at diagnosis could be mostly due to a decreasing efficacy of early diagnosis for patients under 60 years old and to less effective therapies for older patients.
基于人群的生存率的时间趋势和地理差异的解读通常并不容易，这是因为难以区分观察性偏倚、诊断和治疗程序及其相互作用的影响。相对生存率的描述性分析通常基于自诊断以来固定时间点估计的生存水平，而解读问题可以从对所考虑的相对生存率的形状分析中受益。本文应用允许估计治愈患者比例的参数生存模型，根据年龄和诊断时期来分析和讨论欧洲国家之间结肠癌相对生存率的差异。结肠癌患者的生存曲线根据两个参数来描述：治愈患者的比例和致命病例的平均生存时间。这些参数通过对欧洲癌症登记（EUROCARE）项目出版物中得出的相对生存值进行最小二乘非线性回归来估计。指数生存函数和威布尔生存函数用于对致命病例比例的相对生存曲线进行建模。威布尔模型通常比指数模型拟合得更好，这表明致命病例的死亡率自诊断后随时间下降。然而，对于最年轻的患者，这两种生存函数给出的估计值实际上相互重叠。据估计，欧洲结肠癌患者中被治愈的总体比例为38.6%。这一比例在1978 - 1980年诊断的患者中为36%，在1983 - 1985年诊断的患者中为40%。相应地，致命病例的平均生存时间从1.18年增加到1.52年。按年龄来看，治愈患者的比例从年轻患者（15 - 44岁时为48.4%）到中年患者（55 - 64岁时为38.6%）显著下降，从中年患者到最年长患者（75岁及以上时为34.4%）仅略有下降。致命病例的生存时间则呈现相反的趋势，即同一年龄组分别为1.71年、1.75年和0.77年。各国治愈病例的比例和致命病例的平均生存时间往往呈正相关。我们的结果与1978 - 1985年期间欧洲结肠癌生存率确实有所提高的假设一致，也表明诊断时相对生存率随年龄增长而下降这一众所周知的现象，可能主要是由于60岁以下患者早期诊断的有效性降低以及老年患者治疗效果较差。
