Deep-sea bacteria, the promising new prostate cancer treatment

Women may have breast cancer as their number one (in fact, breast cancer is the commonest cancer in the UK, despite the fact that 99% of people diagnosed with it are women) but men have no room for complacency. In the USA, prostate cancer is the second most common cancer among men after skin cancer, and there are 2 million prostate cancer survivors. In the UK, it’s the commonest form of cancer and the second commonest cause of cancer death among men, with about 46,000 men diagnosed every year.

There’s huge variability between different prostate cancers in terms of aggressiveness. The chance of cancer progressing is measured by a combination of factors – how far it’s spread at diagnosis, the grade of cancer (type of cells found) and the level of a blood test called PSA. For ‘intermediate’ and ‘high risk’ cancers, radiotherapy or surgery are the treatments of choice for most – sometimes with hormone therapy alongside. But both of these carry significant risks of long-term side effects, including erectile dysfunction for most and incontinence for a significant minority. Clearly this is preferable to the alternative for most men, but it’s obviously much less than ideal.

Some men have a ‘low risk’ cancer, where the preferred treatment is ‘active surveillance’ – no treatment on the spot, but regular follow-up so doctors can step in if there are signs of progression before it’s too late. The theory is that because quite a lot of ‘low risk’ cancers are very slowly progressive, they may never do any harm and this approach avoids unnecessary treatment, with all the side effects this entails. But determining how low risk a cancer is isn’t an exact science and failure to step in runs the risk of the cancer spreading. So the holy grail would be a treatment that offered all the benefits of current treatment (long-term life with no recurrence of the cancer) without the side effects.

A study this week suggests the holy grail may not be such an impossible dream. The trial involved a new technique called vascular-targeted photodynamic therapy, using a drug developed from deep-sea bacteria which live in complete darkness. The drug, padeliporfin, only becomes active in the presence of light. The 413 men in the trial all had ‘low risk’ cancers. Half of them received the treatment and their cancer progression was assessed 2 years later and compared to that of the other 200 men who were under active surveillance. This sort of trial is called a Randomised Controlled Trial, and is generally accepted as the ‘gold standard’ for testing treatment effectiveness.

Before being given the drug they had an MRI scan to check the position of their cancer. They then had a general anaesthetic, during which laser fibres were placed precisely at the site of the cancer. When the lasers were switched on, the drug was activated, but there was little damage to healthy prostate tissue.

By two years later, 14% of men who didn’t get treatment were cancer-free (as measured by prostate biopsy) and in 30% of men, the cancer had progressed enough for radical treatment to be needed. By contrast, only 6% of men treated with the experimental drug needed further treatment, and 49% were cancer free. What’s more, most side effects of the treatment were mild and lasted less than 2 months.

These results look very promising, but they don’t yet tell us that the treatment is suitable for all. All but 5 of the men were white, and none had moderate or high risk cancers, so we don’t know if treatment would work in the same way for them. And while many men with low risk prostate cancer opt for active surveillance, some choose surgery or radiotherapy – and this study tells us nothing about how vascular-targeted photodynamic therapy compares with these treatment options. What’s more, the follow-up was only 2 years, so we can’t be certain the same benefits will be maintained in the longer term.

So more studies will be needed, and this treatment isn’t going to be available in the short-term. But for a cancer which causes so much devastation, this deep-sea treatment is definitely a step in the right direction.

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