目的：分析本院鼻咽癌病人接受放射治療後，產生第二原發癌症的發生率及分析可能的危險因子，我們也同時分析病人得到第二原發癌症之後的預後。材料及方法：從1971年4月至2009年4月，共有1367位新診斷鼻咽癌病患於本院接受放射治療，其中的位得到第三原發癌症，他們接受了不同的治療方法，包含單純手術或合併放射治療，同步放射化學治療或單純放射治療。放射治療的技術包含了傳統的放射治療，三度空間順形放射治療(3DCRT)及強度調控放射治療(IMRT)。结果：最常見第二原發癌症的部位依序是頭頸癌，肺癌，肝癌，血癌及淋巴癌。對所有病患而言，發生第二原發癌症的中位數時間為放射治療後94個月，粗發生率為3.3%，追蹤二十年後發生第二原發癌症的累積機率為16.7%，在接受傳統放射治療及包含三度空間順形放射治療或強度調控放射治療兩組發生率的比較，其差異並未達到統計上的意義(p=0.666)。在存活率的比較方面，單獨鼻咽癌或合併第二原發癌症兩組比較亦未達到統計上的意義(p=0.245)。结论：頭頸癌是鼻咽癌病人接受放射治療後最常發生的第二癌症。對於發生第二原發癌症而言，大於50歲的病人較易發生。

Purpose: To define the incidence and risk of the second primary malignancies (SPM) in patients with nasopharyngeal cancer (NPC) post radiotherapy in our hospital. We also analyze their prognosis after the SPM Materials and Method: Between April 1971 and April 2009, 1367 patients were indentified to have NPC after definitive radiotherapy. Of them, 45 patients developed SPM. They received various treatment strategies including surgery with or without adjuvant radiotherapy, concurrent chemoradiotherapy or radiotherapy alone. Radiotherapy technique included conventional radiotherapy, three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT). Results: The most common site for a SPM was the head and neck region, lung, liver and leukemia & lymphoma in decreasing order. The median time to development of SPM was 94 months. The crude incidence was 3.3%. The 20-year cumulative rate of development of SPM was 16.7%. Older patient has a higher incidence of 39.1%. The incidence between patients who received conventional radiotherapy and those having 3DCRT or IMRT is not significantly different (p=0.666). There is no significant difference for survival in NPC with or without SPM (p=0.245). Conclusions: Head and neck cancer is the most common second cancer in NPC patients after radiotherapy. There is a trend to the development of SPM in the older age groups (>50 years old)