Most of CancerLit overlaps MedLine, but this will give you slightly improved coverage of cancer with no extra effort. You can also order article photocopies through PaperChase, although it's not exactly cheap. I haven't yet seen a free MedLine access that I like as much as PaperChase, though they are getting closer all the time. I still recommend that you use an access with a powerful and easy to use interface, such as PaperChase, even though it's going to cost you some money that way. Because the PaperChase interface makes it easier to combine search terms, to limit searches, and helps guide you to the most relevant keywords.
Cancer is usually a matter of life and death - it's worth a few bucks to get the best.
So go ahead and have a look at some of the free MedLine pages out there - but don't hesitate to go for the best. The National Library of Medicine 's PubMed is the preeminent free MedLine. This service is rapidly improving and is definitely worth a try. Start out by taking their tutorial, and experiment to learn the ropes. I guarantee that after playing with these databases for a while you will wish you had some expert help.