PET imaging today: contribution to the initial staging and prognosis of patients with non-Hodgkin's lymphomas

Malignant non-Hodgkin lymphomas (NHLs) are commonly staged according to the Ann Arbor staging system developed for Hodgkin's lymphoma. Recently, new staging modalities including metabolic imaging by positron emission tomography (PET) using F-18 fluorodeoxy-glucose (FDG) have been developed. In the present study, we investigated 77 untreated patients with different histologies of NHL both with conventional imaging techniques and FDG-PET. The patients were classified according to the World Health Organization classification and came from 2 major PET imaging centers in Louisiana and Texas. Seventy-six of 77 cases of NHLs were positive by PET imaging. PET imaging resulted, both in high/intermediate grade and indolent NHLs, in a higher stage in more than 20% of cases. In the subtype of high grade NHL diffuse large B cell lymphoma, upstaging by PET appears to be clinically relevant as a marker for a more aggressive tumor. In low grade NHL, stage changes were less pronounced. PET imaging did not reliably detect all cases of bone marrow involvement (especially in indolent lymphomas). However, even in low-grade NHL, clear indications exist for performing PET imaging. The value, the clinical relevance, and new developments in PET imaging for the different types of NHLs are discussed in detail.