Can one swollen leg mean cancer?

Yes but. Other things are more common than a compressive tumor or cancer leading to a blood clot, especially at 48. Get it checked.
Possibly . There are many things that are possible causes of one swollen leg, so it is important not to presume that it has to be cancer. The best thing to do is to see your doctor and get things checked out so that you know exactly what the cause of the swelling is.