Can the PET scan be misleading?

Positron emission tomography (more commonly referred to as a PET scanning) have seen markedly increased usage by doctors over the past 10 to 15 years. PET is a nuclear imaging technique, used in conjunction with a CT scanner to image for possible cancer and/or metastases. Using FDG, an analog of glucose, the PET scan detects tissue with increased metabolic activity.

In 2001, a meta-analysis by Gould et al. was published, noting a high accuracy in diagnosing metastatic non-small cell lung cancer (94% sensitivity and 83% specificity). However, more recent data indicate PET scans might not be as good as originally thought.

For example, false-positive PET scans may be rampant in Histoplasma-endemic areas, resulting in missed diagnosis of metastatic cancer, which could result in denial of potentially curative surgery. Deppen et al. published a study in 2011 demonstrating that as much as 60% of PET scans suggestive of lung cancer in a Histoplasma-endemic area (Nashville, Tennessee) were in fact false positives.

In another study published in 2011 (Darling et al.), researchers found that PET scans can wrongly diagnosed metastatic disease to the lymph nodes inasmuch as 35% of cases, again resulting in denial of potentially curative surgery.

More recently, analysis of suspected early-stage lung cancer patients who had undergone surgical resection found further areas of concern regarding the PET scan:

1. Although 82% of confirmed cancers had positive PET scans, 69% of benign lesions (mostly granulomatous disease) had positive PET scans.

2. Although there was an 85% probability that a positive PET was cancerous, there was only a 26% probability that a negative PET scan was not cancer.

3. The specificity of PET (avoidance of false positives) was quite low (average 31%) and varied widely depending on the city: for example, in Philadelphia it was 46% and in Birmingham it was only 15%.

 

Although the routine use of PET scanning is recommended for the evaluation of non-small cell lung cancer, it appears that PET is not as good as previously thought. False positive  testing could result in unnecessary resections or denial of curative resection and false negative testing could result in delay of appropriate treatment.

 

References:

Gould MK, et al. Accuracy of positron emission tomography for diagnosis of pulmonary nodules and mass lesions: A meta-analysis. JAMA 2001; 285:914 – 924

Deppen S et al. Accuracy of FDG-PET to diagnose lung cancer in a region of endemic granulomatous disease. Ann Thoracic Surg 2011; 92:428 – 433

Darling GE et al. Positron emission tomography-Computed tomography compared with invasive mediastinal staging in non-small cell lung cancer: Results of mediastinal staging in the Early Lung Positron Emission Tomography Trial. J Thoracic Onc 2011; 6:1367 – 1372

Segerman D, Miles KA. Radionuclide imaging: general principles. In: Adam A, Dixon AK, eds. Grainger & Allison’s Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 7

Ettinger DS. Lung cancer and other pulmonary neoplasms. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 197