Many patients with kidney cancer experience moderate or high temperature, and it often disappears after taking out the affected organ (nephrectomy). It is almost never the sole manifestation of kidney cancer, and it is often accompanied by other symptoms, usually hematuria and flank pain, which is known as the triad of kidney cancer. However, not all patients have the same symptoms, and the disease is highly variable. The cause of fever is not known, but it is probably associated with the vascular involvement of kidney cancer, and it is not necessarily a sign of metastasis.
Needless to say, there are plenty of causes of fever, and most of them are more common than kidney cancer. Thus, even if you have high fever and back pain, do not panic and ask your physician. He might need to rule out kidney stones and pyelonephritis (an infection in the kidneys) before starting to think about other causes.