There is a study from, I believe, the 50's in England on cancer and parts of the body - it was found that workers in coal mines did not have any carcinogens evident on the first three digits of their hands [the ones who smoked]

Lynda, do you remember that study source? Where it is? I wish Rose posted here!

Dr Hueper from 1957
"It is stated that cigarette smoking causes cancer of the lung, but not cancer of the mouth.That privilege is reserved for the smoking of pipes, or cancer of the lip.
Now I don't think that anybody can assert that a cigarette smoker has not intensive contact with whatever comes out of the tip of the cigarette in the region of his lip and the region of the first part of his mouth.
There is also the fact that while other types of tars which are known to be carcinogenic, like coal tar,will cause cancer of the skin.

The hands of tar workers develop skin cancer, the marked drenchings of the fingers, the skin of the fingers which holds the cigarette, which are sometimes deeply brown stained have never so far as I know, developed cancer of the skin.

One of the gentlemen, the proponents of the cigarette theory, has tried to explain that phenomenon by saying that the first three fingers of the right hand of man have a natural immunity against cancer.

Q Who is that?
A Lickint. He takes a very similar role in Germany in regard to that question, as Dr Graham and Dr Wynder have taken here.
Q Let me ask you this, are the skin tissues the same on the hand and the mouth and the lung? Are they all three identical tissues?
A They are not identical tissues but they react the same in response to coal tar."

Niacin is being used in skin creams to protect against skin cancer

Vitamin lotion may help skin cancer fight
"Dermatologists are hoping a lotion containing a common vitamin could be the key to reducing skin cancer rates in Australia.
Scientists have found a cream containing vitamin B3 can significantly increase the skin's ability to stop skin cancers forming.

The results will be presented at an international dermatology conference this weekend.
Even as little as six minutes in the sun can weaken the body's defences against skin cancer.
Researchers at the New South Wales Cancer Institute painted healthy volunteers with a lotion containing vitamin B3 or nicotinamide.

They found those patients treated with the substance suffered no damage to their immunity when exposed to ultra violet light.
In another first, the study found men were twice as likely to suffer immune damage from the sun than women.
Scientists are not exactly sure how vitamin B3 boosts the skin's defences against cancer.

http://www.abc.net.au/news/health/sophie_scott/newsitems/s1366452.htm


This would appear to explain the phenomenon:
Niacin and Niacinamide In Flue Cured Cigarette Smoke Condensate August 10 1960
http://legacy.library.ucsf.edu/action/document/page?tid=pnx69d00&page=1