The Utility of Bayes’ theorem in positron emission tomography positive suspected cases of relapsed non-Hodgkin’s lymphoma

The role of Positron Emission Tomography (PET) in suspected non Hodgkin’s lymphoma (NHL) relapse is not well established. An illustrative case report of a patient with a positive PET scan and suspected recurrence is presented and analyzed using Bayes’ theorem. We find that the positive predictive value (PPV) of the PET scan significantly depends on the patient’s initial prognosis and time from diagnosis. The greater the elapsed time and the better the initial prognosis, the lower the PPV of a positive PET scan. We have developed a reference table to estimate the PPV of a positive PET scan for treated NHL patients with suspected relapse. From this analysis we strongly recommend repeating a biopsy in the vast majority of suspected relapsed NHL patients with a positive PET scan to confirm the diagnosis.