From the Guidelines
A PET scan negative pulmonary nodule is generally considered to have a low likelihood of being malignant, but it is not a definitive exclusion of cancer 1. As a precautionary measure, it is recommended to follow up with a non-contrast CT scan of the chest in 3-6 months to monitor the nodule's size and characteristics.
Key Considerations
- If the nodule is larger than 8mm, a follow-up CT scan should be done in 3 months 1.
- For nodules smaller than 8mm, a follow-up CT scan can be done in 6-12 months.
- Additionally, if the patient has a history of smoking or other risk factors for lung cancer, a more thorough evaluation, including a contrast-enhanced CT scan or a biopsy, may be necessary 1.
- It is also recommended to consider the patient's overall clinical presentation, including symptoms and medical history, when determining the best course of action 1.
False-Negative Results
- False-negative results on PET scan can occur in patients with less metabolically active tumors, including lepidic-predominant adenocarcinomas, mucinous adenocarcinomas, and carcinoid tumors 1.
- False-positive results on PET scan can also occur, often due to infections or inflammatory conditions, including endemic mycoses, TB, rheumatoid nodules, and sarcoidosis 1.
From the Research
Significance of a Negative PET Scan Result
A negative Positron Emission Tomography (PET) scan result for a pulmonary nodule does not entirely rule out the possibility of malignancy.
- The study by 2 found that 18.2% of initially PET-negative solid pulmonary nodules developed subsequent malignancy at an average time of 37.6 months.
- Another study by 3 reported that cancer was diagnosed in 22.4% of the PET-negative subgroup, highlighting the need for continued follow-up.
- The research by 4 and 5 demonstrated the diagnostic value of PET/CT in differentiating benign from malignant solitary pulmonary nodules, but also acknowledged the limitations of a negative PET scan result.
Implications of a Negative PET Scan Result
A negative PET scan result should not be considered a surrogate for tissue diagnosis in the case of non-FDG avid solitary pulmonary nodules.
- The study by 2 emphasized the continued need for follow-up of initially PET-negative nodules beyond the 2 years currently suggested in popular guidelines.
- The research by 3 supported the current surveillance practice of continuing to follow LungRADS-4/PET-negative patients as LungRADS-4 patients, given the high cancer risk despite a lack of activity on PET.
- The study by 6 showed that PET/CT can improve stratification of cancer patients with indeterminate pulmonary nodules, but a substantial number of patients considered at low and intermediate pretest likelihood of malignancy with histology-proven lung malignancy showed abnormal PET/CT findings.
Clinical Considerations
Clinical variables such as nodule location, size, chronic obstructive pulmonary disease, family history of lung cancer, pack-years, and number of years quit in former smokers were not significantly associated with greater cancer risk among the PET-negative subgroup 3.
- The study by 5 found that a negative PET scan is associated with only a 4.7% risk of malignancy, but this risk increases with the patient's age and the size of the nodule.
- The research by 4 and 6 highlighted the importance of considering pretest probability of malignancy and the role of 18F-FDG PET/CT in characterizing indeterminate lung nodules.