Nicotine DOES cause cancer - it gets metabolized into nitrosamines which are carinogenic.
In response to the initial question, although theoretically light cigarettes may have less risk of cancer than regulars cigarettes, studies have shown that the risk of cancer (lung, oral etc) is the same. The theory is that subconsciously your body realizes that there is less nicotine in a light cigarette so you end up inhaling more and for longer.
Hope that helps!
and yeah, you should stop smoking
if you want a good motivator, try this:
Take in a deep breath.
Now try breathing ON TOP of that.
Now imagine that's how you have to breath every day. That's COPD and what your lungs will be like in 30 years if you keep smoking.