Allergic Contact Dermatitis to Gear Shift Knob (Australia)
This was, no doubt, a challenging question. The problem with trying to piece together a story for a guy with a localized contact derm on the hand is that you need some history to pull everything together. If you practice is like ours, most of the time the patient does not present to your office with a known allergen in mind, because if they did, they wouldn't be bothering you with a mystery they've already solved.
In this case, I wanted you to put it all together. Your clues were what you see above, which is a clear case of localized allergic contact dermatitis. Second, I gave you some clues: 1) He was a skin cancer patient 2) It was a localized dermatitis secondary to rubber. At this point (as one of you did) you should be thinking "why did he say skin cancer patient?" and put together that it had to be in a latitude conducive to skin cancer. But wait! There's more! Why the localization to the left hand? Gotta be an answer. That was when our Sherlock figured out that in some countries that were formerly part of the British Empire (or influenced by them as in the Japanese) they drive with the shifter on the left, not on the right. The British Isles are not known for their skin cancer problems, so it had to be either Australia, or New Zealand. Playing the odds, since Australia is much bigger than New Zealand, the answer was Australia.
Australia has a very highly developed derm community, and first among the superstars of Aussie derm is Robin Marks. For a bonus point, what does "Slip, Slap, Slop" mean? Dr. Marks has developed a body of literature which has informed the rest of us on such subjects as which side of the body has more AKs and what is the likelihood an individual AK will turn malignant. Not bad for a country founded as a penal colony...