PET scans in diffuse large B-cell and follicular lymphomas

This article reviewed the role of PET (positron emission tomography) scans in diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL).

PET scans have been used for years to measure cancer activity in patients with DLBCL. Its use in FL has only recently been considered. In an FDG-PET scan, glucose is injected into the patient. The scan measures the rate of glucose uptake by cells. This uptake happens faster in cancer cells. This type of scan can be used to stage the disease at diagnosis, to measure response to treatment, and to determine whether a patient is in remission.

The current study reviewed the use of PET scans over the course of treatment in patients with DLBCL and FL.

Diffuse Large B-Cell Lymphoma

PET scans are a standard part of the staging process for DLBCL. They are very accurate in determining lymph node involvement and the extent of disease. Accurate staging is essential for determining treatment and risk level. The risk level can also be measured by a combination of patient characteristics. The risk levels help to determine the intensity of treatment needed. For example, patients with 4 or more areas of lymph node involvement tend to have worse outcomes than those with only 1 involved lymph node area. In one study, 25% of patients with 4 or more lymph nodes involved were disease progression free at 3 years. This was compared to 79% of those with 1 node involved.

The bulk (size and density) of a tumor has also been used to determine risk. Recently it has been shown that the rate of glucose uptake by a tumor (known as the metabolic tumor volume, or MTV) is a better predictor of outcome than tumor bulk. Studies have used different thresholds, however, for what is considered high or low MTV. Low MTV has been associated with better 3-year progression-free survival (77–92%) compared to high MTV (48–56%). Bone marrow biopsy is also becoming less important. Studies have shown that disease stage based on PET scan is not often changed after biopsy.

PET scans with CT (computed tomography) scans are used to measure remission rates following treatment. Any remaining cancer activity on a scan, along with biopsy results, may indicate the need for further treatment. Patients who have negative scans after treatment generally have long-term remission, or can be considered cured. High-risk patients have a higher chance of relapse.

Recently PET scans have been used early in treatment to measure response. Early response (after 1-4 cycles of chemotherapy) predicts remission at the end of treatment. One study noted that 60% of patients were in remission after 2 cycles of treatment, and these patients all remained in remission at the end of treatment. Another study found, however, that 36% of patients were not in remission early in the study. Of these, 19% achieved remission by the end. Based on these results, it is not recommended to change treatment after an early PET scan.

PET scans after high-dose chemotherapy given before stem cell (immature blood cell) transplantation are also predictive of transplant success.

Follicular Lymphoma

Accurate initial staging for FL is very important for treatment choice. For early-stage disease, radiotherapy is the standard treatment. A relapse in these patients generally occurs outside of the area treated. This indicates that staging was not accurate. Patients with advanced disease without symptoms may not be treated at first (watch and wait), so it is essential that these patients are staged correctly. PET-CT scans have been shown to be more accurate than CT alone in determining sites for radiation. Bone marrow biopsy is necessary in FL patients. Biopsy detected involvement in 43% of patients who did not show bone marrow involvement on CT scan.

PET-CT is also important in determining remission after treatment. In an analysis of 3 studies, including 246 patients, PET scan was better at predicting time to disease progression than CT alone. Average time to progression was 74 months for patients who achieved complete remission compared to 16.9 months for those who did not. The patients could be helped by closer monitoring and different treatment at time of relapse. PET after high-dose chemotherapy may also be useful in predicting success of stem cell transplantation.

This study reviewed the use of PET scans in patients with DLBCL and FL.

This study reviewed the use of PET scans in patients with DLBCL and FL.