Lasers pinpoint the latest weapon in fight against cancer: Photosensitive drugs are being successfully tested on tumour patients. Liz Hunt reports

THE PATIENT had been in the operating theatre since early morning and a large tumour stuck to her abdominal wall had been removed. Under normal circumstances, she would be stitched and despatched to the recovery room, while surgeons hoped they had removed all of the cancerous cells.

Instead, the theatre staff at the Royal London Hospital Trust donned goggles and began the second stage of her treatment, which aims to minimise the chances of the disease returning and spreading to other parts of her body.

Photodynamic therapy (PDT) involves the use of a 'photosensitiser' drug. This accumulates preferentially in tumour cells rather than healthy tissue, but it is not toxic until it has been activated by light of a certain wavelength.

Two days earlier the woman, recently diagnosed as having cancer of the bowel, had been given the drug intravenously. Now a thin arc of fluorescent light invisible to all but the camera lens arched over her body. Norman Williams, professor of surgery, and Dr Mutaz Abulafi guided the laser beam on to the tumour site to activate the drug and destroy any microscopic cancer cells that remained.

Recurrence of bowel cancer is common - as high as 60 per cent in some cases - and often develops rapidly after surgery. In a small trial - the first of its kind - involving 58 patients at the Royal London, 26 had received surgery followed by PDT and the remainder had surgery only. There had been three recurrences in the surgery-only group, and none in the PDT group over more than a year of monitoring.

PDT has been used experimentally in patients around the world to treat cancer of the bladder, lung, and oesophagus, with good results. However, a new generation of photosensitive drugs starting clinical trials should make PDT more effective.

Details of one of the new drugs were presented to cancer specialists at a conference in London yesterday. The drug is more potent - the tumour cells take up a far greater amount of it - and causes fewer side-effects. Existing drugs caused photosensitivity which lasts for six to eight weeks after the operation, and patients must avoid sunlight. Photosensitivity caused by the newer drugs lasts only two to three weeks.

Professor Williams is cautiously optimistic about PDT, but says there is a need for clinical trials to replace the anecdotal evidence.

'It is far too early for us to say that it is the answer for cancer but we know that we can definitely affect tumours. What we have yet to prove is its use as an adjunct to surgery,' he said.

(Photograph omitted)