Integrating PET and PET/CT into the risk-adapted therapy of lymphoma

Imaging with ¹⁸F-FDG PET is increasingly accepted as a valuable tool for lymphoma management. A recent shift in the use of PET and PET/CT in medical practice has become evident. We selected aggressive lymphomas as a platform for the discussion of these imaging modalities in oncology patients and the resulting management questions. Methods: On the basis of our clinical experience and a review of the literature, we evaluated the emerging role of ¹⁸F-FDG PET in staging, response assessment, risk stratification, and tailored therapy. We explored the biologic meaning of true-positive or true-negative PET results in assessing tumor killing and the implications for risk-adapted therapy of lymphoma. Results: PET/CT improves the accuracy of staging and response assessment over that of conventional anatomic imaging. The strong prognostic value of PET for aggressive lymphomas is established, whether the imaging is performed at the end of therapy or after only a few cycles of chemotherapy. How to modify therapy on the basis of PET results is not yet established, although it is clear that high-risk patient subsets can be reliably identified. Conclusion: PET/CT improves the accuracy of staging and response assessment over that of CT alone. A negative midtreatment PET result does not indicate the absence of a viable tumor or that therapy can be abbreviated or reduced in intensity. Similarly, a positive PET result does not necessarily indicate a viable tumor or that extending or intensifying treatment will benefit the patient. In assessing response, it is possible that prognosis rests not only on whether the PET result is positive or negative but also on the intensity of the signal. Although the prognostic value of PET for lymphoma is now clear, how to tailor therapy accordingly is a separate matter that requires further investigation.