Editing Malignant transformation (section)

==Causes==

There are many causes of primary malignant transformation, or [[tumorigenesis]].  Most human cancers in the United States are caused by external factors, and these factors are largely avoidable.<ref name=Doll>{{cite journal |vauthors=Doll R, Peto R |title=The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today |journal=J. Natl. Cancer Inst. |volume=66 |issue=6 |pages=1191–308 |year=1981 |pmid=7017215 |doi= 10.1093/jnci/66.6.1192}}</ref><ref name=Blot>{{cite journal |vauthors=Blot WJ, Tarone RE |title=Doll and Peto's quantitative estimates of cancer risks: holding generally true for 35 years |journal=J. Natl. Cancer Inst. |volume=107 |issue=4 |page= djv044|year=2015 |pmid=25739419 |doi=10.1093/jnci/djv044 |doi-access=free }}</ref><ref name="pmid26271254">{{cite journal |vauthors=Song M, Giovannucci EL |title=RE: Doll and Peto's Quantitative Estimates of Cancer Risks: Holding Generally True for 35 Years |journal=J. Natl. Cancer Inst. |volume=107 |issue=10 |page= djv240|year=2015 |pmid=26271254 |doi=10.1093/jnci/djv240 |doi-access=free }}</ref>  These factors were summarized by Doll and Peto in 1981,<ref name=Doll /> and were still considered to be valid in 2015.<ref name=Blot />  These factors are listed in the table.

{| class="wikitable sortable"
|+ External factors in cancer
! Factor!!Estimated percent of cancer deaths
|-
|Diet     ||  35
|-
|Tobacco     ||  30
|-
|Infection     ||  10
|-
|Reproductive and sexual behavior<sup>a</sup>     ||    7
|-
|Occupation     ||    4
|-
|Alcohol     ||    3
|-
|Sunlight (UV)     ||    3
|-
|Pollution     ||    2
|-
|Medicines and medical procedures     ||    1
|-
|Food additives     ||    <1
|-
|Industrial products     ||    <1
|}
<sup>a</sup> Reproductive and sexual behaviors include:  number of partners; age at first menstruation; zero versus one or more live births