What is the value of PET/CT for treatment response assessment in lymphoma?
A 69-year-old woman with history of chronic obstructive pulmonary disease (COPD) noticed gradually increasing lumps in her neck for about 1 month. She also complained of decreased appetite but denied any history of weight loss, fever or night sweats. She has a 50 pack-year smoking history with no family history of cancer.
Her physical exam was consistent with bilateral cervical lymphadenopathy, greater on the left, and left axillary lymphadenopathy. The liver and spleen were not enlarged. Her blood work was significant for normal blood cell counts and lactic dehydrogenase (LDH.) The initial PET/CT scan showed generalized hypermetabolic lymph nodes, specifically: left supraclavicular lymph nodes, 2.3 cm × 1.1 cm (standard uptake value[SUV], 3.3); non-enlarged bilateral cervical lymph nodes, greater on the left side with varying SUV measuring 2.9 in suprahyoid neck and 2.3 in the infrahyoid left neck; right pretracheal and paratracheal nodal mass measuring 4 cm × 3.2 cm with SUV up to 20.3; aortopulmonary window lymph nodes minimally increased with SUV of 2.3; and left axillary lymph nodes 3.3 cm × 1.6 cm with SUV of 4.6.
In the abdomen, there were scattered hypermetabolic lymph nodes measuring up to 1.9 cm ×1.2 cm in the right common iliac region with SUV of 7. Additional lymph nodes were seen in the small bowel mesentery, measuring up to 1.9 cm with SUV up to 3.
Photos courtesy of M. Ghesani
She underwent left supraclavicular lymph node biopsy consistent with diffuse large B cell lymphoma with clinical stage IIIA disease. Her IPI score was 1 and she was started on standard chemotherapy with R-CHOP. She had an excellent clinical response and interim PET/CT after four cycles of chemotherapy showed a decrease in size and metabolic activity of all the lymph node regions.
She went on to finish a total of eight cycles of chemotherapy, which she tolerated well. A repeat PET/CT at the end of treatment showed continued response to chemotherapy. There were no significant cervical lymph nodes. The left axillary lymph node decreased in size to 1 cm × 0.5 cm with no associated hypermetabolic activity. Also, the pretracheal lymph node decreased in size to 1.4 cm × 1 cm, and there were no significantly enlarged lymph nodes in the abdomen or pelvis. She continues to remain in clinical remission and is in regular follow-up.
The role of PET scans has been widely increasing in the management of patients with lymphoma. The PET/CT systems integrating the functional PET images with anatomic CT images are an important tool in improving the accuracy of PET scan. PET/CT scans have been used for initial staging, restaging, monitoring response to treatment and for follow-up in patients with lymphoma. Some studies have also reported its use in distinguishing indolent from aggressive lymphoma using the degree of metabolic uptake.
Often, it is difficult to distinguish between residual tumor masses and dead, fibrotic tissue that can be seen on routine imaging studies following treatment of lymphoma. PET/CT can help to differentiate these metabolic active tumor masses from nonviable or necrotic tissue, thus avoiding unnecessary biopsies.
Jerusalem and colleagues compared PET findings to classical CT scan in 54 patients with Hodgkins and intermediate/high grade non-Hodgkins lymphoma following treatment. Of 24 patients with residual masses on a CT scan, only five showed metabolic uptake. Also, one of 30 patients with a negative CT scan had positive FDG uptake on PET. All of these six patients relapsed shortly after the completion of treatment compared with relapse in five of 19 patients (26%) who had a residual mass on CT scan with a negative PET. Thus, a positive PET scan at the end of treatment had a higher positive predictive value compared with a positive CT scan (100% vs. 42%).
There is increasing utilization of PET/CT in monitoring the response to treatment in patients with lymphoma. PET/CT performed during the course of treatment can provide important prognostic information. Spaepen and colleagues studied the role of FDG PET/CT scanning during the mid-treatment evaluation of patients with aggressive NHL. Thirty-one of 37 patients with a negative mid-treatment PET/CT remained in prolonged remission, whereas none of the 33 patients with a positive scan had durable remission. This translated into better PFS for patients with negative PET/CT scan (1,059 days compared with 45 days).
Similarly, Haioun and colleagues evaluated the role of early PET in management of 90 patients with aggressive NHL. The 2-year event-free survival and OS were significantly better in patients with early PET-negative disease compared with PET-positive patients (82% vs. 43% and 90% vs. 61%, respectively). However, data are limited as to how to use this information in altering treatment of the patients. This might become an important tool in the future if studies assessing the change in therapy based on interim PET/CT findings could show an improvement in response rates and survival in these patients.
Kevin Becker, MD, is a medical oncology attending at Maimonides Medical Center, Brooklyn, N.Y.
Munir Ghesani, MD, is an associate clinical professor of radiology at Columbia University College of Physicians and Surgeons and attending radiologist at St. Lukes-Roosevelt Medical Center.
Sumit Talwar, MD, is a hematology oncology fellow at St Lukes-Roosevelt Hospital Center.
For more information:
- Haioun C. et al. Blood. 2005;106:1376-1381.
- Jerusalem G. et al. Blood.1999;94:429-433
- Spaepen K. et al. Ann Oncol. 2002;13:1356-1363.