PET/CT speeds sarcoma treatment

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Oncologists often have to wait months before they can determine whether a treatment is working—utilizing PET/CT, researchers at the University of California, Los Angeles, Jonsson Comprehensive Cancer Center have shown that they can determine after a single cycle of chemotherapy whether cytotoxic drugs are killing the cancer or not.

“Imaging tests for early response assessments need to identify responders with a high sensitivity to avoid denying potentially effective treatments to patients,” wrote the authors of the study published in the April 15 issue of the journal Clinical Cancer Research. “Although neoadjuvant therapy may improve the outcome of patients with STS, particularly in the setting of a pathologic response, the currently available treatments are associated with significant toxicities. This toxicity would be minimized if physicians could identify non-responders and switch them to alternative treatment strategies or earlier surgery.”

Baseline, early, and late follow up FDG-PET/CT in a histopathological responder (A) and a non-responder (B). Changes in tumor SUVpeak and tumor sizes are indicated. Image and caption courtesy of Fritz C. Eilber, MD, and the Division of Surgical Oncology, David Geffen School of Medicine at the University of California Los Angeles.

Using a Siemens Medical Systems Biograph Duo PET/CT system, researchers monitored 50 patients undergoing treatment for high-grade soft tissue sarcomas. The patients were receiving neoadjuvant chemotherapy treatments to shrink their tumors prior to surgery. The study found that response could be determined about a week after the first dose of chemotherapy drugs. Typically, patients are scanned at about three months into chemotherapy to determine whether the treatment is working.

“The question was, how early could we pick up a response? We wanted to see if we could determine response after a single administration of chemotherapy,” said Fritz Eilber, MD, an assistant professor of surgical oncology, director of the Sarcoma Program at UCLA’s Jonsson Cancer Center and senior author of the study. “There’s no point in giving a patient a treatment that isn’t working. These treatments make patients very sick and have long-term serious side effects.”

For the study, Eilber and his team monitored the tumor’s metabolic function; to identify an effective response to treatment, researchers stated that they needed to see a 35 percent decrease in the tumor’s metabolic activity.

Of the 50 patients in the study, 28 did not respond to their initial chemotherapy and Eilber and his team were able to determine this within a week of their initial treatment through the utilization of PET/CT.

“The significance of this study was that it identified people--more than half of those in the study--who were not going to benefit from the treatment early in the course of their therapy,” Eilber said. “This information significantly helps guide patient care. Although this study was performed in patients scheduled for surgery, I think these findings will have an even greater impact on patients with inoperable tumors or metastatic disease as you get a much quicker evaluation of treatment effectiveness and can make decisions that will hugely impact quality of life.”

Eilber said he was surprised how soon response to therapy could be determined.

“We had an idea that patients either respond or do not respond to treatment, but we weren’t sure how early you could see that,” he said. “I really was not sure we would be able to see effectiveness this early.”

Eilber and his team will continue to follow the patients and a clinical trial currently is underway based on the results of this study. Eilber believes it will help personalize treatment for each patient and may one day become the standard of care.

Researchers also may use PET/CT to gauge response to novel and targeted therapies. Eilber said that they are clinically testing new tracers as well.  Instead of measuring glucose uptake, these probes look at cell growth. Response to therapy also may be tested using PET in other cancer types, he said.

The nearly two-year study, funded by grants from the UCLA In Vivo Cellular and
Molecular Imaging Centers and the U.S. Department of Energy, represented a true multidisciplinary effort, Eilber said. Experts from surgery, medical oncology, molecular and medical pharmacology, radiology, pathology, orthopedics, nuclear medicine and biostatistics comprised the research team.