Approximately 85% of metabolically active pulmonary nodules are malignant.² FDG-positive pulmonary nodules should be assumed to be malignant until proven otherwise. Exceptions to this rule include postinflammatory lesions such as sarcoidosis, granulomatous conditions, inflammation, infection, and adenomas. Solitary pulmonary nodules that are FDG-negative include bronchoalveolar cancer, scar adenocarcinoma, carcinoid tumors, and neuroendocrine tumors (partly avid).

• Breast cancer. FDG-PET/CT can be used for staging and restaging, though local staging is performed mainly with MRI and mammography. It can also be used to monitor response to therapy and to plan radiotherapy.

One study found that FDG-PET was 88% sensitive and 80% specific for breast cancer. False-negative results were returned for 12% of all breast cancer cases.³

• Lymphoma. Applications include initial diagnosis and staging, assessing response to therapy and monitoring residual disease, identifying recurrent disease, seeking out suitable sites for biopsy, disease surveillance, radiotherapy planning, and prognostic stratification.

A comparison of PET/CT and contrast- enhanced CT when assessing organ involvement in lymphoma found the sensitivity of the two modalities to be 88% and 50%, respectively. The specificity of PET/CT was 100%, while contrastenhanced CT was 90% specific.⁴

False-positive results can be due to infection, inflammation, FDG uptake in cardiac muscle or the bowel, and thymic hyperplasia. Mucosa-associated lymphatic tissue lymphoma, lymphocytic non-Hodgkin’s lymphoma, chronic myelogenous leukemia, and other nonaggressive lymphomas can lead to falsenegative diagnoses.

• Esophageal cancer. Many etiological factors have been shown to be associated with esophageal cancer. Smoking and excessive alcohol intake are believed to contribute directly in many cases.

The two main histological subtypes are squamous cell cancer, which primarily affects the upper two-thirds of the esophagus, and adenocarcinoma, which normally is found in the lower third of esophagus. Predisposing factors include Barrett’s esophagus, gastroesophageal reflux, and possibly previous mediastinal radiotherapy.

ROLE OF FDG-PET/CT

FDG-PET/CT is useful in the following:

• Preoperative staging to identify nodal and disseminated metastases;
• Demonstration of recurrent disease and assessment of response to therapy, including neoadjuvant chemotherapy; and
• Prediction of therapy response and overall prognosis.

False-negative results may be due to small T1 lesions, local nodes applied close to the primary tumor, or linitis plastica. Peritoneal metastases may be missed on PET if they are very small, but they are then often detected on CT. Gastritis, Barrett’s esophagus, esophagitis, a normal contracted stomach, and physiological uptake in the gastric outlet can lead to false-positive diagnoses.