利用低劑量電腦斷層篩檢早期肺癌：系統性文獻回顧和統合分析

Use of Low-Dose CT for Early Lung Cancer Screening: A Systematic Review and Meta-Analysis

目標：近年一個美國政府主導的大型隨機分派研究發現，針對重度抽菸者每年進行低劑量電腦斷層篩檢肺癌，相較於僅接受胸部X光篩檢者，三年內可相對降低20％肺癌死亡率；本文欲探討背後潛在的風險以及應用在台灣本土的適切性。方法：將過去10年針對此議題的研究進行系統性回顧（Systematic Review），蒐集每個研究的相關數據以及可能影響診斷工具效用的因子，再藉由統合分析（Meta-analysis）計算敏感度、陽性預測率等。結果：僅有5篇研究提供較完整追蹤資料，可推估低劑量電腦斷層的敏感度為87.43％（95％ CI：72.79％～94.77％）、與特異度為96.45％（95％ CI：80.39％～99.44％）；而由19篇文獻提供的資料，陽性預測率估計約為6.4％（95％ CI：4.8～8.2％）。結論：雖然美國許多學會根據近年文獻紛紛建議對肺癌高危險群以低劑量電腦斷層篩檢肺癌，但過低的陽性預測率較少被強調，以目前的流程篩檢下來會造成許多的偽陽性個案，這會造成很多篩檢者被迫要面臨結果不確定性的壓力，甚至是接受不必要的侵入性切片或手術。尤其台灣肺癌發生率僅約美國一半，且女性抽菸比率較歐美國家低，而目前也未能確定台灣肺癌的主要危險因子，因此貿然大規模效仿美國指引進行篩檢，會導致更低的陽性預測率。因此，如何發展出適合台灣本土的建議，則是目前這個領域需要克服的難題。

Objectives: Recent studies have demonstrated that low-dose computer tomography (LDCT) screening in place of X-ray screening for lung cancer could reduce relative mortality in heavy smokers by 20%. The aim of this study was to conduct a systematic review and meta-analysis for the performance of LDCT in lung cancer screening and to evaluate the potential benefits and harms of implementing such a screening program in Taiwan. Methods: We searched electronic databases (MEDLINE, EMBASE and Cochrane library) for studies on LDCT screening (1996 to 2014) and conducted meta-analyses of sensitivity, specificity, and positive predictive values (PPV). We also undertook meta-regression to examine the impact of study characteristics on LDCT screening. Results: Only 5 studies provided sufficient information for a meta-analysis of sensitivity (87.43%, 95% Confidence Interval [CI]: 72.79 to 94.77%) and specificity (96.45%, 95% CI: 80.39% to 99.44%). Twenty-one studies provided information for a meta-analysis of PPV (6.4%, 95% CI: 4.8 to 8.2%). Conclusions: Several studies from Western countries recommended the use of LDCT screening for lung cancer in high risk populations, especially for heavy smokers. However, the low PPV of LDCT was seldom discussed. Those false positive cases may suffer from mental stress and harm from unnecessary invasive interventions. Given the low smoking prevalence in Taiwan, implementing LDCT for population screening in lung cancer could represent a significant challenge.