The isotopes most commonly used in brachytherapy, in which radioactive metal beads are placed next to a tumour, are iodine-125, iridium-192 and phosphorus-32, and the most commonly treated cancers using the technique are cervical, prostate, breast and skin. IsoRay Medical is bucking both trends.
Shares in the Richmond, Washington-based nanocap rose 17% yesterday after trial data showed that its caesium-131 brachytherapy seeds halted regrowth of 19 of 20 recurrent tumours. Though brachytherapy is an established form of radiotherapy the delivery technique used was new, and the trial hit ought to be a fillip for a company hoping to make the leap into profitability.
Seeds of destruction
The data, presented at the Society of Neuro-Oncology’s Conference on Meningioma, in Toronto, Canada, come from 16 patients with meningiomas. Though these tumours are usually benign, the trial patients had had recurrences after both surgery and external beam radiation treatment and were considered to be at an increased risk of further recurrence.
The caesium-131 brachytherapy seeds were embedded in collagen and applied directly to the brain tissue after the tumour was resected. IsoRay says this is an advantage over external beam radiotherapy as treatment starts immediately; there is often a gap of a few weeks between surgery and traditional radiotherapy.
After treatment there was no radiographic evidence of regrowth of 19 of the 20 tumours. Two of the patients had radiation side effects in the brain, which IsoRay says has been a major problem in the past for patients who have undergone repeated treatments for brain cancer.
IsoRay’s technique, called GammaTile, has been under development for some time: IsoRay presented trial data in gliomas, meningiomas and brain metastases two years ago with similar results. It remains unapproved.
IsoRay has developed a number of forms of caesium-131-based radiotherapies including the Proxcelan brachytherapy seeds for the treatment of prostate, lung and head and neck cancers, among others. But it is perhaps best known for the GliaSite system, which it acquired from its developer Proxima Therapeutics in 2011.
This involves the insertion of a balloon catheter into the brain immeditately after surgical removal of a tumour. As the patient recovers from the surgery, the balloon is inflated with a liquid form of caesium-131. The inflated catheter stays in place for between three and seven days, during which the patient can be released from hospital.
Compared with GliaSite, IsoRay’s brachytherapy beads are far more familiar. It is intriguing that GliaSite has gained FDA clearance while the GammaTile product has not. Shareholders appear to think that it might soon.