Investigations may be required for several reasons.
If you have seen blood in the urine or even if your doctor has detected microscopic blood in your urine that you cannot see, you will need specific urine tests to look for possible cancer cells in the urine as well as a urine test to exclude simple infections. It is mandatory to also undergo scans of your abdomen to look for any cancers in the kidney as a cause for the bleeding. Although the risk that an early cancer will have spread to other parts of your body is very rare, a scan of the abdomen may also detect if any of the lymph nodes are involved. This is not usually the case. Blood in the urine would also mandate an inspection of your bladder with a telescope as some types of kidney cancer can be associated with bladder cancers and these need to be identified.
If a cancer in the kidney has been diagnosed as an incidental lesion or mass at the time of a scan to investigate other symptoms, often you do not need any further specific investigations. Obviously you will need to have a consultation with the Urologist to determine the best form of treatment which would requires surgery to remove either the lump itself if it is small or possibly the entire kidney if it is large.