Urinary Anatomy continued...
Under conditions of chronic inflammation, such as infection of the bladder with the Schistosma haematobium parasite, squamous metaplasia may occur in the bladder; the incidence of squamous cell carcinomas of the bladder is higher under conditions of chronic inflammation than is otherwise seen. In addition to transitional cell carcinomas and squamous cell carcinomas, adenocarcinomas, small cell carcinomas, and sarcomas can form in the bladder. In the United States, transitional cell carcinomas represent the vast majority (over 90%) of bladder cancers. However, a significant number of transitional cell carcinomas have areas of squamous or other differentiation.
Carcinogenesis and Risk Factors
There is strong evidence linking exposure to carcinogens to bladder cancer. The most common risk factor for bladder cancer in the United States is cigarette smoking. It is estimated that up to half of all bladder cancers are caused by cigarette smoking and that smoking increases a person's risk of bladder cancer two to four times above baseline risk.[2,3] Smokers with less functional polymorphisms of N-acetyltransferase-2 (known as slow acetylators) have a higher risk of bladder cancer than other smokers, presumably because of their reduced ability to detoxify carcinogens.
Certain occupational exposures have also been linked to bladder cancer, and higher rates of bladder cancer have been reported in textile dye and rubber tire industries; among painters; leather workers; shoemakers; and aluminum-, iron-, and steelworkers. Specific chemicals linked to bladder carcinogenesis include beta-naphthylamine, 4-aminobiphenyl, and benzidine. Although these chemicals are now generally banned in Western countries, many other chemicals still in use are also suspected of causing bladder cancer.
Exposure to the chemotherapy drug cyclophosphamide has also been associated with an increased risk of bladder cancer.
Chronic urinary tract infections and infection with the parasite S. haematobium have also been associated with an increased risk of bladder cancer, often squamous cell carcinomas. Chronic inflammation is thought to play a key role in carcinogenesis in these settings.
Bladder cancer typically presents with gross or microscopic hematuria. Less commonly, patients may complain of urinary frequency, nocturia, and dysuria, symptoms that are more common in patients with carcinoma in situ. Patients with upper urinary tract urothelial carcinomas may present with pain due to obstruction by the tumor.
It is important to note that urothelial carcinomas are often multifocal—the entire urothelium needs to be evaluated if a tumor is found. In patients with bladder cancer, upper urinary tract imaging is essential for staging and surveillance. This can be accomplished with ureteroscopy, retrograde pyelograms during cystoscopy, intravenous pyelograms, or computed tomography (CT) urograms. Similarly, patients with an upper urinary tract transitional cell carcinoma have a high risk of developing bladder cancer; these patients need periodic cystoscopy and surveillance of the contralateral upper urinary tract.