Utility of 18-FDG-PET Scanning in Lymphoma by WHO Classification

Reviewer: M. Kara Bucci, MD
The Abramson Cancer Center of the University of Pennsylvania
Last Modified: December 8, 2001

Presenter: Rebecca L. Elstrom

Background:

18-FDG-PET scanning is an important imaging modality in the staging and monitoring of many malignancies, including lymphoma. Some tumors, however, do not have the high glucose uptake needed for 18-FDG uptake, and are therefore not well imaged by PET. In order to assess whether the histologic subtype of a lymphoma is related to its visibility by PET imaging, this retrospective analysis of PET scans was performed at the University of Pennsylvania. The author's assessed PET positivity of newly diagnosed and untreated relapsed lymphoma by WHO classification of the tumors.

Materials and Methods

Of >600 PET scans performed on patients with lymphoma, 155 cases had pathologic data available for correlation.
By histologic subtype of these 155:

48 diffuse large B-cell lymphomas (LBCL)
37 follicular lymphomas (FL)
40 Hodgkin's lymphomas (HL)
12 marginal zone lymphomas (MZL)
7 mantle cell lymphomas (MCL)
2 cutaneous B-cell lymphomas (CBCL)
2 anaplastic large T-cell lymphomas (ALCL)
4 peripheral T-cell lymphomas (PTCL)
1 mycosis fungoides (MF)
1 Burkitt-like lymphoma (BLL)

Results:

Overall, 144/155 (93%) scans were positive.
PET imaging was considered "informative" in all 144 cases with positive scans.
By histologic subtype:

100% of CBCL, FL, MCL, ALCL, BLL, and MF cases showed increased 18-FDG uptake.
40/41 (98%) HD, 7/12 (58%) MZL, 1/4 (25%) PTCL, and 0/2 (0%) CBCL cases demonstrated increased 18-FDG uptake.
100% of low grade lymphomas (FL, MCL) were PET-positive.

Author's conclusions:

For the most common histologic subtypes (LBCL, FL, HD, MCL), PET scanning was informative.
For less common lyphoma subtypes (PTCL, MZL, CBCL) PET scanning was less reliable.
The abnormal metabolism of glucose that leads to a positive PET scan may not be part of the malignant transformation of the non-reliably PET-positive lymphomas.
Histologic grade (as opposed to WHO subtype) may not be the most important factor determining PET-positivity.

Clinical/Scientific Implications:

PET is emerging as an important imaging modality in lymphoma, and may be more often indicated in the histologic subtypes that are reliable PET-positive.
Studies evaluating the role of altered glucose metabolism in malignancy are underway.