PROBLEM TO BE SOLVED: To contain a nucleotide removal / repair inhibitor having a simple chemical structure which is easily available in a large amount, having a strong activity of inhibiting the removal / repair of damaged nucleotides, having low toxicity and high safety. Provided are enhancers and antitumor agents used for the treatment of tumors that damage the DNA of tumor cells such as primary tumor cancer cells. The following lactone compound (1) And the following naphthoquinone compound (3) Or one containing a pharmaceutically acceptable salt thereof. Tumor treatment enhancers and antitumor agents contain this nucleotide excision repair inhibitor as an active ingredient. [Selection diagram] None【課題】大量に入手し易く、簡素な化学構造であって、損傷を受けたヌクレオチドの除去修復を阻害する活性が強くて、毒性が低く安全性が高いヌクレオチド除去修復阻害剤、それを含有し原発巣の癌細胞のような腫瘍細胞のＤＮＡを損傷させる腫瘍治療のために用いられる増強剤及び抗腫瘍剤の提供。【解決手段】下記ラクトン化合物（１）と、下記ナフトキノン化合物（３）、又はそれの薬学的に許容される塩を含有するもの。腫瘍治療の増強剤及び抗腫瘍剤は、このヌクレオチド除去修復阻害剤を、有効成分として含有するものである。【選択図】なし
