One of the main tools that oncologists use to image cancer is the positron emission tomography (PET) scan, an imaging test that uses a small amount of radioactive sugar to detect metabolically active areas in the body.
CU Cancer Center member Sarah Milgrom, MD, recently conducted research to investigate whether PET scans could help predict Hodgkin lymphoma recurrence. She used the images to measure the lymphoma volume for each patient at the time of diagnosis, then followed the patients over time to find out whether the initial metabolic tumor volume was related to the risk of the cancer coming back. Her findings, which led to her being selected for a Young Investigator Award from the Children’s Oncology Group, may help cancer doctors more accurately predict patients’ risk of recurrence, which in turn may help them choose the most appropriate treatments.
We spoke with Milgrom about her research and what it means for patients.
Q: How do PET scans work?
A: Before the scan, a small amount of radioactive sugar is injected into a vein. This sugar, or radiotracer, collects in parts of the body that are metabolically active because they absorb a lot of sugar. The PET scanner then takes detailed pictures of the body, showing areas that have absorbed large amounts of the radiotracer. PET scans are commonly used in many types of cancer, including Hodgkin lymphoma. Hodgkin lymphoma cells take up more sugar than normal cells, so they are detected by PET scans. In this way, PET scans can pinpoint the locations of the lymphoma in the body.
Q: What was your hypothesis regarding PET scans in your study of metabolic tumor volume in children and adolescents with intermediate-risk Hodgkin lymphoma?
A: We wanted to see if the volume of disease in a patient’s body at the time of their diagnosis was associated with their risk of recurrence after treatment. For this study, we looked at patients with intermediate-risk Hodgkin lymphoma who were treated in a Children’s Oncology Group (COG) study. We only included patients who received the same chemotherapy and radiation regimen. We used PET scans to measure lymphoma volume for each patient at the time of diagnosis, and we examined whether initial metabolic tumor volume was associated with the risk of cancer recurrence.
Q: What were your findings?
A: We found that greater lymphoma volume at diagnosis was associated with a greater risk of recurrence after treatment. Importantly, metabolic tumor volume was associated with risk of recurrence, even when controlling for other key variables such as stage, mass, and response to chemotherapy. These are the risk factors currently used to select the right treatment for patients. This means that the metabolic tumor volume can add prognostic information on top of standard risk factors so that it can be used to select the best treatment for patients.
Q; What does this research mean for future patients?
A: In the future, it is possible that baseline metabolic tumor volume measurements will be used to select the most appropriate treatment for patients with intermediate-risk Hodgkin lymphoma. This could lead to better patient outcomes.
Q: You did a similar study in children with high-risk Hodgkin lymphoma. How did it work?
A: That study included patients treated according to a different COG protocol intended for patients with high-risk Hodgkin lymphoma. According to that protocol, patients received different treatments depending on how quickly their disease responded to chemotherapy. Patients whose disease had responded very well after the first two cycles of chemotherapy were referred to as “rapid early responders” and received less intensive therapy than patients whose disease had not responded as well at that time (“slow early responders” ). Again, we used PET scans to measure the initial lymphoma volume for each patient to investigate whether that volume was associated with the risk of cancer recurrence. First we evaluated the whole group and then we looked at the fast early responders and the slow early responders separately.
Q: What were your findings in the study in high-risk patients?
A: We found that total lesion glycolysis – a measure that takes into account the total body volume of the disease and its metabolic activity – was significantly associated with the risk of recurrence in the total cohort. However, when we looked at the fast early responders and the slow early responders separately, we came to a very interesting finding. Total lesion glycosis was associated with the risk of recurrence in fast early responders, but not in slow early responders.
Rapid early responders with a low tumor burden at baseline had excellent results with less intensive therapy; however, fast early responders with a high baseline tumor burden experienced poor outcomes that were even worse than those of slow early responders. This suggests that patients with a high initial tumor burden may benefit from more intensive therapy, even if they achieve a rapid early response.
Q: What will your research on high-risk Hodgkin lymphoma mean for patients in the future?
A: PET-based measures of initial disease burden can help us predict patient recurrence risk. That, in turn, could help us select the best treatment for patients with high-risk Hodgkin lymphoma.
Q: Will using PET scans to measure the initial burden of disease change the way doctors care for cancer patients?
A: Currently, quantitative PET parameters are not used in routine clinical management. One reason is that it takes a lot of time and effort to perform the measurements. An active area of research is the optimal approach to obtain these measurements easily and quickly. Once these technical aspects are worked out, I believe that PET-based volumetric parameters will become the routine measure of baseline disease burden that contribute to risk-based treatment strategies in Hodgkin lymphoma.
Pediatric Blood and Cancer
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