Five-year cancer survival rates are widely reported and often interpreted to mean that early detection saves lives, that a late fatal diagnosis would have been prevented by earlier detection, and that increasing survival over time proves better treatment. This expository article explains why such inferences are not supported by survival statistics alone. A simple Markov model of tumor progression, calibrated to patterns like those in SEER data, shows that high survival after early diagnosis, large gaps between early and late stage, and improving survival can all appear even when treatment is ineffective and screening does not reduce mortality. The discussion ties these points to the clinical literature and argues that randomized trials and mortality outcomes are needed to support screening and treatment claims; five-year survival alone provides little actionable evidence and is easily misread.

翻译：五年癌症生存率被广泛报告，并常被解读为早期检测能挽救生命、晚期致命诊断本可通过更早发现而避免，以及生存率随时间提升证明了治疗手段的改进。这篇解释性文章指出，上述推论无法仅凭生存统计数据得到支持。一个基于肿瘤进展的简单马尔可夫模型（经校准以匹配SEER数据库中的典型模式）表明：即使治疗无效且筛查未降低死亡率，早期诊断后的高生存率、早期与晚期之间的巨大差距以及生存率的提升仍可能同时出现。本文结合临床文献讨论这些观点，并强调筛查和治疗主张需要随机对照试验及死亡率结局作为支撑；仅凭五年生存率无法提供可操作的证据，且容易被误读。