Smoking leaves an archaeological record of the hundreds of DNA mutations it causes, scientists have discovered.
Having sequenced thousands of tumour genomes, they found a 20-a-day smoker would rack up an average of 150 mutations in every lung cell each year.
The changes are permanent, and persist even if someone gives up smoking.
Researchers say analysing tumour DNA may help explain the underlying causes of other cancers.
Pamela Pugh, 69, was diagnosed with lung cancer in 2013. She started smoking aged 17 and quit in her early 50s.
But she said: Even though I gave up many years ago, the effects of smoking caught up with me.
Had I known as a teenager that smoking caused mutations which would stay with me for life then I would never had started.
The study, in the journal Science, was carried out by an international group, including the Wellcome Trust Sanger Institute in Cambridgeshire and the Los Alamos National Laboratory in New Mexico.
The analysis shows a direct link between the number of cigarettes smoked in a lifetime and the number of mutations in tumour DNA.
The authors found that, on average, smoking a packet of cigarettes a day led to:
150 mutations in each lung cell every year
97 in the larynx or voice box
23 in the mouth
18 in the bladder
six in the liver
Joint lead author Prof Sir Mike Stratton, from the Wellcome Trust Sanger Institute, said: The more mutations there are, the higher the chance that these will occur in the key genes that we call cancer genes, which convert a normal cell into a cancer cell.
There are 35,000 deaths a year in the UK from lung cancer, and it is estimated that nine out of 10 cases are preventable.
科学家研究发现，吸烟会导致DNA突变，给人留下数百种基因突变的永久记录。
在对数千个肿瘤基因组进行测序后，科学家发现每天吸烟20支的人每年每个肺细胞累积平均有150个基因突变。
这些突变是永久且持续的，即使吸烟者戒烟也不可逆。
研究人员说，分析肿瘤DNA能帮助解释其他癌症的深层原因。
69岁的帕梅拉-皮尤2013年被诊断患有肺癌。她自17岁开始吸烟，近50岁时戒烟。
但她说：尽管我很多年前就戒烟了，但吸烟的影响一直在。
如果年轻时我知道吸烟导致的基因突变一生都会跟随着我，那么我绝不会开始吸烟。
这项研究发表在《科学》期刊上，由一个国际研究组研究得出，包括英国剑桥郡的基金会桑格研究院，以及美国新墨西哥州的洛斯阿拉莫斯国家实验室。
研究显示，人一生中吸烟的总数量和肿瘤DNA变异的数量之间存在直接关系。
研究作者发现，平均来讲，每天吸一包烟会导致：
每年每个肺部细胞中有150个基因突变。
喉部或喉头97个突变
口腔部位23个突变
膀胱18个突变
肝脏6个突变
研究报告的合作主创者、来自基金会桑格研究院的迈克-斯特拉顿教授说：突变越多，关键基因，也就是我们所说的癌症基因发生突变的几率也就越大，这会将正常细胞转变为癌细胞。
英国每年有3.5万人死于癌症，据估计其中九成可以预防。