Interim PET-CT in the management of diffuse large B-cell lymphoma

Once the diagnosis of diffuse large B-cell lymphoma has been established, physicians and patients would like to know if a given treatment regimen is likely to succeed-if the patient can be cured or if at least a durable remission is achievable. This desire has lead to efforts to use interim positron emission tomography (PET) scanning as part of risk-adapted therapeutic clinical trials. In general, these studies use a variable number of doxorubicin-based induction cycles with rituximab, followed by the interim PET. If the test is negative, treatment is continued, but if it is positive, therapy is changed to treatment that concludes with autologous stem cell transplantation. Results of studies for interim PET have yielded mixed and confusing results, with high negative predictive value but positive predictive value ranging from 20%-80%. To use interim PET scanning effectively, clinicians need simple (positive or negative) criteria that are easy to interpret, reproducible, and have a high positive and negative predictive value so that we can be certain that by not changing therapy if the test is positive, we are not doing the patient a disservice.