Lets say i have a tumor on the left side of my back near the spine can it cause pain down the back of my right leg?

Possible,not likely: It depends on tumor type, size and location. Leg pain(radiculopathy) from the back comes from the same side as the lesion. A tumor that has encroached upon the spine can cause opposite side pain if it has crossed the midline.

See answer: Tough to say what is happening in your particular case, but tumors can certainly cause referred pain in several areas. The inflammation from the tumor, if it extends to the r side, may cause problems in that leg.