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

Background:

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.

Results:

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.