During the past ten years great progress has been made in the pathology of renal growths. Uncertainty and confusion existed in our knowledge of their nature previous to that time. At present the diagnosis of renal tumor or cancer will not suffice. Microscopic examination must be carried out in every case, and growths should not be reported in the incomplete manner formerly the custom. We now know that the tumors or new growths of the kidney belong to two groups: The benign, including the fibromata, the lipomata, adenomata and angiomata; and the malignant, that includes the carcinomata and sarcomata. An intermediate class is formed by the so-called Grawitz tumors, which may occur in a circumscribed form as benign or in a more diffuse manner as a malignant tumor. These various forms will be taken up in detail later.
In regard to the frequency of renal tumors, one author found only