Men who have had gonorrhoea are twice as likely to develop bladder cancer, a study has found.
Infection with the Gonorrhoea bacterium is linked to cancer
Researchers analysed the histories of 286 bladder cancer cases and confirmed a link between the sexually transmitted infection and cancer.
In total, the Harvard School of Public Health team examined detailed health records on 51,529 US men.
Writing in the British Journal of Cancer, they said inflammation caused by gonorrhoea could be the key.
Dr Dominique Michaud, Assistant Professor of Epidemiology and lead author on the paper, said: "Two studies have previously suggested a link between gonorrhoea and bladder cancer in men.
"But these were retrospective studies - meaning information on gonorrhoea history was gathered after the cancer was diagnosed.
"These studies can sometimes give misleading results."
This study was done prospectively - the cases chosen had full gonorrhoea histories available before the study started.
It is the first time such a prospective study has confirmed the link.
Dr Michaud said: "Gonorrhoea is an infection that often recurs, causing local inflammation and symptoms such as incomplete emptying of the bladder.
"The inflammation itself or the associated symptoms could be contributing to the development of bladder cancer."
Professor John Toy, medical director of Cancer Research UK said: "This study strengthens the suspected link between infection with the gonorrhoea bacterium and bladder cancer in men.
"The next step is to confirm whether the increased risk could be caused directly by the gonorrhoea infection or its symptoms.
"Further research is also needed to exclude the possibility that gonorrhoea is acting as a marker for the real cancer-causing agent, such as a separate infection.
Although the number of new patients each year is falling, gonorrhoea is the second most commonly diagnosed bacterial sexually transmitted infection in the UK and the new study emphasises the importance of protecting against such infections.
Dr Gwenda Hughes, head of STI surveillance at Health Protection Agency said:
"According to our latest annual figures of all STIs, Gonorrhoea decreased by 13% (from 22,350 in 2004 to 19,495) in 2005.
"However, we should not be complacent and overall figures of STIs are increasing.
"Quick diagnosis is essential, so anyone who thinks they may have put themselves at risk of contracting an STI or has developed symptoms should seek advice from their GP or go to a GUM clinic as soon as possible."