The silent killer

Dr Dinesh Mavinahalli Gangaiah writes about how aggressive bladder cancer can get as it accounts for the second-highest tobacco cancer-related death next only to lung cancer

Bladder cancer is the tenth most common and thirteenth deadliest neoplasm in the world. The urinary bladder is a hollow muscular organ situated in the pelvis which collects urine from the kidney until micturition. The urinary bladder is lined by urothelial cells that can flatten to accommodate high volumes of urine stored. The next layer of the urinary bladder consists of smooth muscles that relax to accommodate and store urine and contract to void urine during micturition. Almost 90% of bladder cancer arises from urothelial cells and commonly referred to as bladder cancer.

Bladder cancer constitutes approximately 2.1% of all cancer deaths and is the second leading cause after lung cancer in tobacco-related cancer mortality. The prognosis of bladder cancer mainly depends on gender and stage of cancer. The mortality rate among men is 3.2/100000 men while it drops to
0.9/100000 for females. The stage of cancer determines the prognosis of the patient. In-Situcarcinoma refers to cancers that are limited only to the urothelial lining of the bladder. These patients constitute a 5-year survival of 95.8% and represent 51% of all cases of the urinary bladder.

However, in India, early-stage disease at presentation is seen less often than in western countries. The 5-year survival continues to drop further as cancer grows through the wall of the bladder. The 5-year survival of 69.5% is seen when the disease is limited within walls of the bladder but has grown beyond the lining epithelium. The 5-year survival further drops to 36.3% when the disease spreads to draining lymph nodes and only 4.6% survival when the disease is spread to other non-regional organ sites. Although the incidence of bladder cancer has been steadily decreasing, the mortality rate due to bladder cancer has plateaued over the recent decades. Muscle invasive bladder cancer refers to those cancers that have grown through the muscle layer of the bladder and these comprise 26-36% of urinary bladder cancers and portend worse outcomes than superficial tumours. Muscle invasive tumours must be considered as aggressive tumours with lower survival and a higher chance of recurrence after treatment.

Found more in men than women

Tobacco is the leading cause of urinary bladder cancer. 70% of bladder cancers are attributable to tobacco, with the association being both dose and duration dependent. Industrial workers, those in leather and textile industries, shoemakers, and hair dye handlers are also more prone to urinary bladder cancers. Across the world, bladder cancer is four times more among men than women. This discrepancy is attributed to differential rates in smoking and industrial workers being mostly men. The prevalence of bladder cancer is 86.4% vs 13.6% between men and women in India. The difference is widened in India with a male: female incidence ratio of 8.9:1 to 3:1 or 4:1 among western countries. The excess frequency of bladder cancer among men can be attributed to higher smoking habits and industrial-related work which is more in men and estrogen-progesterone hormonal influence in the female reproductive period. With a decrease in smoking incidence due to stricter government policies and more women taking up smoking habits, the male: female difference in incidence is gradually narrowing.

Tobacco smoke consists of beta–naphthylamine and polycyclic aromatic hydrocarbons which get metabolised and cleared from the body through the kidney. The metabolites accumulate in the urine and hence in the bladder for a prolonged time. The tobacco metabolites promote carcinogenesis along the lining of the urinary bladder. The disparity is not only in incidence but also in bladder cancer-related mortality.
(The author is a surgical oncologist.)