Case of the Quarter—July 2011

FDG-PET/CT Plays a Key Role in Confirming Diagnosis of Large B-Cell Lymphoma

Patient History
The patient is a 71-year-old male who presented with asymptomatic microhematuria on routine physical checkup. CT scan of the abdomen/pelvis revealed an incidental lung nodule in the right middle lobe. A subsequent CT scan of the chest revealed a 1.7 x 1.9 cm right upper lobe nodule, an 8 mm right middle lobe nodule, and several small subcentimeter right lower lobe nodules. The patient is a former smoker (18 pack-years). He had no dyspnea, hemoptysis, fevers, chills, or night sweats. Based on these CT findings, a brain MRI and FDG-PET/CT were ordered.

FDG-PET/CT Findings
FDG-PET/CT revealed an FDG-positive lesion in the right upper lobe with SUV>13 (Figure 1). Also noted was a smaller right middle lobe nodule with mildly increased FDG activity. An area of activity was noted in the sella turcica with an associated mass. Additionally, a small soft tissue nodule posterior to the left kidney had an SUV of 4 (Figure 2).

figures

Follow-Up
Brain MRI revealed a mass in the sella turcica, which was biopsied and found to be pituitary adenoma. CT-guided biopsy of the nodule posterior to the left kidney revealed diffuse large B-cell lymphoma. Based on these results, the patient underwent video-assisted wedge biopsy of the right upper lobe nodule and right lower lobe nodule, which revealed large B-cell lymphoma. The patient was seen by medical oncology, and a bone marrow biopsy showed no evidence of lymphoma involvement. He subsequently began a course of chemotherapy.

How Did FDG-PET/CT Help?
FDG-PET/CT played a key role in this case by helping to confirm an unusual presentation of large B-cell lymphoma. The PET/CT detected an FDG-avid soft tissue nodule behind the left kidney which was found to be large B-cell lymphoma. Prior to the PET/CT scan, the working diagnosis was that of metastatic lung cancer given the chest CT findings.

Discussion
Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin's lymphoma. Up to one-third of all lymphoma cases are due to DLBCL. It is most commonly found at nodal sites; however more than 50% of patients demonstrate extranodal involvement at time of diagnosis. Diffuse large B-cell lymphoma can arise in the mediastinum, lung parenchyma, or pleura.

FDG-PET/CT is routinely used to evaluate treatment response during chemotherapy1. One systematic review of 311 DLBCL patients undergoing FDG-PET for interim treatment response assessment demonstrated a sensitivity of 78% and specificity of 87%2. Regarding detection of recurrent DLBCL in patients with complete remission after first-line chemotherapy, FDG-PET/CT had a positive predictive value of 0.853. Patients >60 years old and patients with symptoms suggestive of relapse were significantly more likely to have a relapse. As such, in patients <60 years old with symptoms of relapse or in patients >60 years old with or without symptoms of relapse, FDG-PET/CT may be very beneficial in detecting recurrent DLBCL.

1. Seam, P., et al. "The role of FDG-PET scans in patients with lymphoma."Blood, 110:3507-3516, 2007.
2. Terasawa, T., et al. "Fluorine-18-Fluorodeoxyglucose Positron Emission Tomography for Interim Response Assessment of Advanced-Stage Hodgkin's Lymphoma and Diffuse Large B-Cell Lymphoma: A systematic review. "Journal of Clinical Oncology, 27(11):1906-1914, 2009.
3. Petrausch, U., et al. "Risk-adapted FDG-PET/CT–
based followup in patients with diffuse large B-cell lymphoma after first-line therapy." Annals of Oncology, 21(8):1694-1698, Aug. 2010.

Materials for this case study were developed by Dr. Erica M. Giblin, Thoracic Surgeon, Holy Family Hospital.

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