I really really think if they were calling to tell you it is cancer or anything serious, they would not make you wait a week and it probably wouldn't even be just a phone appointment. If it was serious at all they would tell you to come in, in person, right away. I would say don't worry, but I know that's literally impossible for us who suffer.

Also use this as a learning lesson to realize that all the little things we worry about aren't serious at all when something that scares us really bad (like this) comes up. But please don't sit around thinking it's cancer. Again, they wouldn't make you wait a week for that kind of news.