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Study finds photodynamic therapy for vertebral metastases is safe and feasible

Jul 23, 2019

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A Sunnybrook-led study published recently in Clinical Cancer Research found that using photodynamic therapy (PDT) to target vertebral spine metastases is safe and feasible. It’s believed to be the first trial of its kind to use PDT to target spinal metastases in patients.

PDT is a biological treatment with two components. First, a photosensitizer drug is given to the patient and next, light of a specific wavelength is delivered to the tumour. This activates the PDT effect by creating free radical oxygen species that causes cell death.

PDT has been used to treat skin lesions and non-melanoma cancers. The challenge in treating spinal metastases has been directing light to specific anatomic areas deep inside the body.

“We decided to leverage one of our other existing procedures — vertebral cement augmentation (VCA) for example vertebroplasty or balloon kyphoplasty — which allows us to insert optical fibres to deliver laser light to the tumour,” explained Dr. Albert Yee, orthopaedic spine surgeon and lead on this study.

The building blocks of the spine can be threatened by cancers that have spread to the spine, putting patients at risk for breaks, fractures and potential damage to the surrounding normal nerves. VCA looks to stabilize the spine. It’s typically a day procedure that involves injecting bone cement into the building blocks via a bone needle, which is about 3 to 4 mm in diameter and 5 inches long.

“In VCA we already have the bone needle in place in the tumour bed. For this trial we used the same needle to deliver laser light and PDT prior to injecting the bone cement,” explained Dr. Yee.”

The patient receives the photosensitizer drug intravenously 15 minutes prior to light delivery. Tumours uptake this drug more than healthy tissue. Under image-guidance in the operating room or interventional radiology suite, an optical fibre is then inserted via the bone needles into the tumour, and a precise wavelength of light subsequently delivered. Then, the team proceeds with the VCA.

“The cementation is stabilizing the mechanical structure of the spine, and the PDT is ablating the tumour,” Dr. Yee says.

The Phase I clinical trial with 30 patients found the procedure safe from an initial pharmaceutical as well as neurologic perspective and the concept was feasible. Dr Yee is now looking to set up a Phase II trial, where the team will examine the potential effectiveness of the treatment and patient outcomes.

He says he’s hopeful this new treatment approach will soon offer more choice for patients facing spinal metastases.

“We have many treatment options - immunotherapy, chemotherapy, bone strengthening drugs, radiation, surgery. PDT could add another tool to our toolbox to treat these cancers,” he said. “You can apply PDT repeatedly as necessary, and it may be helpful in situations where patients have reached radiation dose limits and/or where other standard local treatments haven’t been successful.”

“My hope is that in future we can work even more with patients and oncologists to help determine what is best for them.”

This trial was completed in collaboration with Dr. Elizabeth David, Dr. Arjun Sahgal, Dr. Ed Chow, Dr. Shane Burch, Dr. Cari Whyne and others at Sunnybrook, as well as members of the Wilson Lab at Princess Margaret Hospital.