The Big Question: Are we on the brink of a breakthrough in the fight against prostate cancer?
Why are we asking this now?
Scientists funded by Cancer Research UK have found seven new genetic variations that are linked with the development of prostate cancer and can raise a man's risk of developing the disease by up to threefold. This is the largest number of genetic risk factors to be uncovered by a single genome-wide study and represents a major advance in understanding the genetic basis of the disease. Six other genetic variations have also been linked with prostate cancer in two separate studies published simultaneously in the current issue of the journal Nature Genetics.
What does this advance mean for prostate cancer?
It means we are closer to having a genetic test for the disease that could predict who is at risk. Those identified could then be targeted for regular screening and early treatment – in theory. One test, called deCODE and marketed by an Icelandic company at £250, has already been launched that checks for the presence of eight of the gene variations but it has been dismissed by rival researchers as "premature". Cancer Research UK scientists say any genetic test raises difficult ethical and practical issues which must be addressed first, such as how men at high risk should be counselled and how often they should be tested for the presence of the disease. Their own test is not expected to be ready for three to four years.
How big a problem is prostate cancer?
Very big and getting worse. It is the commonest male cancer, with 35,000 new cases and 10,000 deaths a year. As a killer of men it is second only to lung cancer and not far short of breast cancer, which kills around 12,500 women a year but gets far more attention and at least 10 times more research funding. Its incidence is rising rapidly, partly because doctors have begun to look for it and are finding cancer that in the past would have gone undiagnosed. It runs in families – if you have a relative with the disease your own risk is doubled, and if he was diagnosed before 60 it raises your risk almost four- fold. There is an urgent need for an accurate test that can tell who is going to get prostate cancer and who will die from it without treatment.
What is the prostate and what are the symptoms of prostate cancer?
It is a gland, only present in men, surrounding the urethra, the tube that carries urine from the bladder to the penis. It is the size of a walnut and produces the semen in which the sperm, made in the testicles, can swim. In one in three men in middle age, the prostate becomes enlarged, causing symptoms such as difficulty in urinating, a weak stream or increased frequency. However, in nine out of ten cases the cause of the symptoms is benign. Only in one out of ten is it cancer.
How is it detected?
With difficulty. The first thing a GP will do for a patient who complains of the above symptoms is check to see if the prostate is enlarged, which can be simply done by inserting a finger in the rectum and feeling it through the bowel wall. The next stage is a blood test for prostate specific antigen – the PSA test – which, if raised, may indicate the presence of cancer. That is followed by a biopsy, a procedure in which a hollow needle is inserted through the penis to take samples of tissue from the prostate to check for cancerous cells.
Is prostate cancer different from other cancers?
Yes, in one crucial respect – more men die with it than from it. It is curable but may not need treatment. This is because in many men it is slow growing – so slow that they can live with it without ill effects and die of something else. However, some prostate cancers are aggressive. This makes determining who is at risk complicated – even when cancer is diagnosed it is not obvious what should be done. The biggest risk factor for prostate cancer, as with other cancers, is age. Most men are diagnosed in their 70s.
How reliable is the PSA test?
Not as reliable as patients or doctors would like. A high reading indicates possible cancer and normally triggers the next stage – a biopsy. But research shows that seven out of 10 men with a high PSA test will not have cancer. Worse, two in a hundred with a low reading will have significant cancer. So a lot of men will receive treatment (a biopsy) they don't need and some will not receive treatment that they do.
Even so, isn't it worth men in middle age being screened?
Men may have good reasons for taking a PSA test – symptoms such as difficulty urinating, or a family history. But they need to ask themselves what they will do if the results are high. The biopsy is a painful, invasive procedure.
If cancer is found, it may lead to surgery, which carries risks, and/or radiotherapy and chemo-therapy which have side-effects. But the cancer may not need treating. In those cases, PSA testing and the treatment it triggers will have caused pain and anxiety and no health benefit.
Even the professor who developed the PSA test in 1987, Thomas Stamey, said in 2004 that it was "all but useless". His discovery spawned a vast prostate screening industry in the US, where more than 250,000 men are diagnosed with the cancer each year. But Prof Stamey now says the test merely indicates the size of the prostate and may do more harm than good by encouraging over-treatment.
Are better tests and treatments likely?
Yes. The latest research has identified two genes that offer scientists new targets. One, called LMKT2, codes for a signalling protein called kinase which is also altered in some other cancers and against which drugs are already being developed.
The second gene, called MSMB, codes for a protein whose level in the blood falls as prostate cancer develops, raising the possibility that it could provide a new more accurate blood test for the disease to replace the PSA test.
The most urgent need is for a means of distinguishing the "tigers" – aggressive, fast growing prostate cancers – from the "pussy cats" – slow growing cancers which need no treatment. Scientists are getting better at telling them apart and recommending treatment or "watchful waiting", in which the progress of the cancer is regularly monitored. But there is still a lot further to go.
Can prostate cancer be beaten?
* A new genetic test will enable men at high risk to be identified for regular screening
* More accurate blood tests based on a new gene target could mean earlier identification of the disease
* Treatment could be offered to those men with fast-growing, aggressive cancers
* The existing PSA blood test cannot distinguish between a cancerous prostate and a benignly enlarged one
* Even when cancer is diagnosed there is often no way of knowing if it needs treating
* Prostate cancer is unique in that it can be so slow to develop that more men die with it than from it
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