Introduction

Two types of cancer arise from the renal parenchyma: renal cell carcinomas and nephroblastomas. Renal cell carcinomas (also known as renal adenocarcinomas and previously as hypernephromas) are confined to adults. Nephroblastomas (Wilms’ tumours) are developmental in origin and present in infancy or early childhood (Ch. 51). Occasional benign renal tumours also occur, e.g. oncocytoma, adenoma and angiomyolipoma (see Box 36.1).

Tumours of the transitional cell epithelium lining the urinary tract (urothelium) are very common. They may arise anywhere in the tract, including the renal pelvicalyceal system, the ureters, the bladder and occasionally the urethra. Pelvicalyceal tumours are uncommon but occur frequently in some parts of the world, e.g. Balkan nephropathy. These urothelial carcinomas, previously known as transitional cell carcinomas, occur exclusively in adults and most commonly in the bladder. Squamous cell carcinomas sometimes occur in the urinary tract and probably arise from metaplastic squamous epithelium, caused by chronic irritation from stones or schistosomiasis. Squamous cell carcinomas also arise occasionally in squamous epithelium at the urethral meatus. Very rarely, an adenocarcinoma develops in the bladder from glandular epithelial remnants of the embryological urachus, or a sarcoma may develop from connective tissue elements.

Pathology of renal cell carcinoma

Renal cell carcinoma accounts for about 3% of adult malignancies and is twice as common in males as females. It rarely develops before puberty but may occur at any age thereafter, with the peak incidence between 50 and 70 years. Renal cell carcinoma mainly occurs sporadically but there are rare familial forms such as von Hippel–Lindau disease. The only proven environmental risk factor is tobacco use.

Renal cell carcinoma originates in renal tubules. Tumour cells are characteristically large and polygonal, with clear cytoplasm representing accumulation of glycogen and lipid. For this reason, these tumours are sometimes known pathologically as clear cell carcinomas. In other variants, the cells are granular and stain more intensely.

Renal cell carcinomas vary in grade of malignancy. Small isolated tumours are often found incidentally at autopsy. Many pathologists regard tumours of less than 2 cm as virtually benign as they rarely display invasion or metastasis. Bilateral tumours are present in about 5%. Large tumours invade surrounding tissues and may metastasise to para-aortic lymph nodes. Advanced renal cell carcinoma characteristically extends into the lumen of the renal vein and into the inferior vena cava (‘tumour thrombus’—see Fig. 36.1). Distant spread is typically to lung, liver and bone. Lung metastases are often typical discrete ‘cannonball secondaries’. Isolated metastases occasionally develop in the brain, bone and elsewhere.

Staging of renal cell carcinoma

Stage I tumours are confined by the renal capsule; stage II tumours have penetrated the renal capsule but remain confined by Gerota’s perinephric fascia; stage III tumours have renal vein involvement or nodal spread; stage IV have distant metastases.

Clinical features of renal cell carcinoma

The classic presentation is with the triad of haematuria, a mass and flank pain; although all three features only occur in about 15% of cases (see Fig 36.2), one is present in 40% of patients. Commonly, diagnosis is made incidentally by discovering a tumour on ultrasonography or CT scanning. Renal cell carcinomas often become large before diagnosis owing to their retroperitoneal position; unfortunately, tumours larger than 8 cm have an 80% chance of having already metastasised. Common and uncommon presenting features of renal cell carcinoma are summarised in Box 36.2.

Approach to investigation of suspected renal cell carcinoma

Ultrasound investigation reliably distinguishes simple benign cysts from solid masses most likely to be tumours, and can demonstrate tumour thrombus in the inferior vena cava. CT scanning is used to stage the disease by assessing invasion of perinephric tissues and by demonstrating regional lymph node or liver metastases (see Fig. 36.3).