“Incidental Carcinomas” Detected by PET/CT Scans In the Patients with Malignant Lymphoma: A Single-Center Experience with 363 Patients

18F-fluorodeoxyglucose-positron emission tomography (18F-FDG-PET) scans or combination of computed tomography (CT) have been clinically standardized as an essential assessment modality in the field of oncology. A major advantage of PET/CT scans over conventional radiologic imaging techniques is its functional ability to distinguish between benign tumors or necrotic lesions (or fibrosis) and malignant diseases. Due to the recent application of PET scans, the concept of the complete remission/unconfirmed established by international working group (IWG), was eliminated in 2007 by themselves. According to the IWG revised response criteria for malignant lymphoma, PET scans have been recommended for pretreatment staging and response assessment in potentially curative patients with diffuse large B-cell lymphoma and Hodgkin's lymphoma. However, these modalities are also associated with false-positive findings (attributed to infection or inflammation), and are known to be affected by glucose metabolism. Moreover, depending on the type of lymphoma, the body-wide distribution of non-Hodgkin's lymphoma can be quite variable and often unexpected. In addition, incidental findings of carcinomas have been reported during routine interpretation of PET/CT. Therefore, the purpose of this study was to evaluate second primary carcinomas incidentally detected by PET/CT for more accurate assessment of patients with malignant lymphoma.

Retrospective analysis was performed on 363 patients (203 male and 160 female) with a mean age of 59.9 years (range of 16–93 y) with malignant lymphoma who underwent a total of 519 consecutive PET/CT scans in our institution from April 2008 through March 2010. All PET/CT scans for initial staging, restaging, response monitoring (mid-treatment) and post-therapy surveillance were included in this study. Brief clinical information including patient characteristics, disease status and treatments were provided to radiologists in advance.

Of the 363 patients, 14 (3.9%) were recommended by radiologists for further investigation in order to evaluate suspicious new abnormalities on the basis of PET/CT findings. Three of the 14 cases did not receive further investigation due to a hematologist's recommendation. Three cases had pathologically proven benign tumors (granuloma, lyomyoma and adenomatous change in thyroid). The remaining eight patients (2.2%) had pathologically confirmed second primary carcinomas, consisting of four colon cancers, three lung cancers, and one pancreatic cancer. The accuracy for detection of the second carcinomas by PET/CT in the present study was excellent (72.7%). No patients had any symptoms due to second carcinomas. Two cases were diagnosed at the first staging, and the others were detected following the chemotherapy for lymphoma. PET scans revealed high accumulations in six of eight patients (75%) despite of no anatomical changes by conventional CT scans. Of note, all of focal intensities in the colon were identified as colon carcinomas (adenocarcinoma), and all patients underwent potentially curative surgery or endoscopic resection.

The present study suggests that early intervention can potentially achieve detection and cure of second malignancies that are incidental findings by PET in malignant lymphoma. This is the first report that evaluated the unexpected lesions detected by PET/CT scans, which were diagnosed as second primary carcinomas, in the patients with malignant lymphoma.

No relevant conflicts of interest to declare.