Positron Emission Tomography with 18F-FDG in the Evaluation of Post-Treatment Residual Mass in Patients with Malignant Lymphoma.

Reviewer: William Levin, MD
The Abramson Cancer Center of the University of Pennsylvania
Last Modified: December 8, 2001

Presenter: Ralph Naumann
Affiliation: University Hospital, Dresden, Germany


  • Management of residual mass after lymphoma treatment is a problematic issue for oncologists.
  • It is not easy to determine if such masses represent active malignant disease or scar tissue that requires no further treatment.
  • Positron emission Tomography (PET) with FDG (a radiolabeled sugar molecule) is a nuclear medicine study that is able to detect areas of active cancer by showing areas of increased sugar metabolism.
  • In the current study investigators looked at the utility of PET in identifying active or recurrent disease after treatment.

Materials and Methods

  • 58 patients with primary or recurrent pathologically proven lymphoma and were included.
  • The minimum interval between end of treatment and PET scan was 4 weeks after chemotherapy and 10 weeks after radiation therapy.
  • FDG uptake was quantitized by standardized uptake values (SUV's). An SUV >3 was called "positive" and highly suspicious for active lymphoma.A "negative" study showed no evidence of FDG uptake and a "questionable" study had a SUV of < 3.
  • For follow-up, PET positive residues were either removed surgically or followed clinically with CT scans at short intervals.
  • Endpoints of study were either clinically or histologically confirmed recurrence or sustained complete response(CR) during the follow-up period.


  • 36 patients with Hodgkin's Disease and 10 patients with NHL had negative PET scans.
  • For those patients with Hodgkin's Disease and a positive PET 1 of 4 patients had recurrence 13 months after the end of therapy, the other 3 patients continued to have CR's and were therefore classified as false positives.
  • For those Hodgkin's patients with questionable PET scans (3 patients) 1 remained in CR and 2 had follow-up scans turn negative.
  • All four patients with non-Hodgkin's lymphoma(NHL) and a positive PET had clinically detected or CT documented recurrence.
  • The one NHL patient with questionable PET scan had disease recurrence.
  • PET scans were 88% sensitive and 68% specific for detecting disease recurrence.
  • If all questionable PETs were classified as negative then specificity went up to 94%.
  • Of all patients with a positive PET, 5 of 8 had recurrence, versus 2 of 50 patients who had a negative PET.

Author's conclusions:

  • FDG-PET could be used as a helpful component in assessing lymphoma patients after therapy.
  • Negative PETs are highly predictive for the absence of disease recurrence.

Clinical/Scientific Implications:

  • PET is another imaging modality that may be useful in detecting active cancer in lymphoma patients.
  • But interpretation of such studies is difficult and requires the expertise of a nuclear medicine specialist.
  • As this study shows, PET scans are not specific for cancer and entities such as inflamation and infection can also result in a "positive" scan.