BY STEPHANIE STEMMLER

Many of us are familiar with the most common strategies for treating cancer: surgery, chemotherapy and radiation therapy. But in the past two decades, new, more targeted treatments have been developed.

One such innovation combines diagnostic testing with therapy to form a type of treatment called theranostics. This therapy uses specially engineered radioactive tracers, called radiopharmaceuticals, in combination with advanced imaging techniques. Working together, these two elements not only find and map cancer cells throughout the body, they also serve as a beacon, lighting a path that cancer-destroying drugs can follow. It’s a one-two punch delivered directly to cancer cells.

“The power behind radiopharmaceuticals is their ability to maximize the tumor radiation dose while minimizing collateral damage to healthy tissues,” explains Hyun Kim, MD, radiation oncologist at Siteman Cancer Center, based at Barnes-Jewish Hospital and Washington University School of Medicine, and co-director of the Theranostics Center. “While traditional, external beam radiation must pass through healthy tissue to reach the tumor, radiopharmaceuticals travel directly to the tumors, even when they are distributed throughout the body. Since the radiation dose only travels millimeters, this allows radiopharmaceuticals to be a powerful, focused radiation treatment option.”

“Theranostics operates the way a key and lock do,” says nuclear medicine radiologist Vikas Prasad, MD, director of the Clinical Theranostics Program at Washington University School of Medicine’s Mallinckrodt Institute of Radiology (MIR). “We design a radiopharmaceutical that looks for a certain biomarker on the surface of cancer cells and, once found, the radiopharmaceutical then inserts itself into that biomarker.”

After the radiopharmaceutical tracer is administered via injection into the blood stream, specialists use scans to visualize the cancer cells detected by the tracer. “When we can see what we need to treat,” Prasad says, “we can then treat what we see.”

Jeff Michalski, MD, Washington University radiation oncologist at Siteman, adds: “We take SPECT/CT (single photon emission computerized tomography/computerized tomography) scans of the patient over a period of days.” That series of images, he notes, “allows us to determine whether there has been uptake of the tracer into the cells. We can also see how quickly the tracer disappears.” Armed with that knowledge, he and colleagues can predict whether the patient may benefit from treatment with a cancer-killing agent and can identify the amount of drug needed.

Any cancer cell that has a known biomarker on its surface potentially can be treated with radiopharmaceuticals, provided there is sufficient blood supply to the site to deliver the drugs. Farrokh Dehdashti, MD, director of the Division of Nuclear Medicine at MIR and co-leader of the Oncologic Imaging Program, has studied novel radiotracers for three decades, conducting early clinical trials of several tracers developed at Washington University. Dehdashti notes: “The field of theranostics has provided patients with therapy that allows for personalized management and treatment of their cancers. This type of therapy can be effective and can improve patient outcomes, even when the disease is very advanced.”

Michalski served as principal investigator for clinical trials evaluating the first targeted radiopharmaceuticals for prostate cancer. Right now, the use of radiopharmaceuticals to treat prostate cancer is approved only for patients with metastatic, castration-resistant prostate cancer who have failed other treatments. “As we move through more clinical trials, we want to determine whether we can use these radiopharmaceuticals earlier and prevent people from progressing to later stages of disease. We’ll also be evaluating whether we can customize the dosage of drugs to each patient based upon their disease progression as seen in imaging,” Michalski says.

Theranostic-based treatment doesn’t work for all patients with cancer. Currently, it’s available only as a third or fourth line of cancer treatment, after other options have failed. Also, use of radiopharmceuticals to treat cancer is approved only for prostate cancer, thyroid cancer and the treatment of neuroendocrine tumors. And, despite the proven success of theranostics’ ability to locate and destroy cancer cells, in one-third of patients, the cells don’t take up the designed tracer, meaning that administration of a cancer-killing drug likely won’t succeed.

That’s why more research is needed. Already, U.S. trials are evaluating radiopharmaceuticals that can detect biomarkers for more cancers, including leukemia, brain tumor, liver cancer, melanoma and breast cancer.

“In one to two years, we’ll see theranostics become an even stronger option for cancer treatment,” Prasad says. “And in five years, I envision its use in 10 or more cancer types, as well as its use as a therapy in combination with immunotherapy treatments.”

“It’s exciting to see how rapidly this field is evolving,” Prasad adds. “The gate is wide open.”