腫瘤指標是癌細胞的產物，或是身體對於癌細胞產生的反應。腫瘤指標通常是蛋白質，可在血液、尿液、糞便或其他體液中偵測到。近年來，血液中的游離DNA，亦已成為精準醫學領域中非常重要的腫瘤指標。
　　腫瘤指標具有五種潛在性功能: (1) 在無症狀之族群篩檢出早期癌症；(2) 診斷癌症；(3) 判斷預後；(4) 監測對於抗癌治療之反應；(5) 偵測癌症復發。
　　以腫瘤指標作為篩檢早期癌症之工具，有下列優點:  (1) 對於受檢者造成之不便、痛苦或傷害極小；(2) 使用自動化儀器，可在短時間內檢測大量檢體；(3)以數據呈現結果，判讀較客觀；(4) 便宜 (游離DNA例外，但游離DNA通常不用於腫瘤篩檢)。然而腫瘤指標作為篩檢早期癌症之工具亦有其缺點，包括: (1) 缺乏特異性，大部份腫瘤指標在良性疾病也可能上升；(2) 在早期腫瘤敏感度低。
　　在演講中，將介紹目前重要的腫瘤指標，包括糞便潛血、甲型胎兒蛋白、人類絨毛膜促性腺激素、攝護腺特定抗原、CA-125、CEA、CA 19-9、CA 15-3、NSE、Pro-GRP、SCC、診斷多發性骨髓瘤之monoclonal immunoglobulin及其他腫瘤指標，並將討論在精準醫學領域非常重要的腫瘤指標-游離DNA。
　　Tumor markers are products of cancer cells, or molecules produced by the body in response to cancer. They are usually proteins, and can be found in blood, urine, stool or other body fluid. Recently, circulating cell-free DNA (cfDNA) has become a tumor marker in the field of precision medicine.
　　 Tumor markers can be potentially used to: (1) screen for cancer in asymptomatic subjects; (2) diagnose cancer; (3) establish prognosis; (4) monitor treatment response; (5) detect relapse.
　　The advantages of tumor markers in cancer screening include: (1) minimal inconvenience or harm for subjects, (2) automated assays that allow processing large quantity of samples in a short time, (3) quantitative results with objective endpoints, and (4) low costs, except for cfDNA which involves expensive technology. However, cfDNA is usually not used in cancer screening.
　　Disadvantages of using tumor markers in cancer screening include: (1) lack of specificity, as many tumor markers are elevated in benign diseases, and (2) low sensitivity, as tumor markers are often not elevated in early stage of cancers.
　　In the lecture the most useful tumor markers, including fecal occult blood, alpha-fetoprotein, human chorionic gonadotropin, prostate-specific antigen, CA-125, CEA, CA 19-9, CA 15-3, NSE, Pro-GRP, SCC, monoclonal immunoglobulins and other markers would be reviewed. Use of cfDNA in cancer patients as a precision-medicine approach would also be discussed.