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Positive PET lung scan
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Positive PET lung scan

Dear Dr, my mother aged 71 was found to have a 1.8cm stellate leision in the right lung on CT described as being highly suggestive of primary malignancy.  A subsequent FDG PET scan showed the leision to "Light up" but not very brightly said the Dr. That was six months ago and a further CT indicated the leision did not grow in size. Her specialist wants to do another CT in June this year, a fine needle biopsy was canceled due to confusion from medications she was on for a sacral fracture.  Essentially my question is what are the odds this will be cancer under these findings. She smoked 100 pack years.
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The diagnosis of lung lesions is routinely made by anatomic conventional imaging with plain chest radiographs.  If no old films are available, additional imaging, with CT, can also be useful.  More recently FDG-PET is used to differentiate benign from malignant pulmonary lesions on conventional studies.  The rationale for using PET with FDG for tumor imaging is based on a fundamental property of tumors: Increased glucose metabolism distinguishes malignant tumors from benign lesions.  The radioactive tracer used is fluorine-18 fluorodeoxyglucose (FDG).   Malignant lesions have a high metabolism, and most will actively accumulate the tracer.
The results from these studies have been consistent, with an overall accuracy around 90%.  Lesions with increased PDG uptake (a positive PET scan) are considered malignant until proven otherwise.  However, not all lesions with increased FDG uptake are malignant.  False positive scans (positive PET scans that prove benign) have been reported with infectious and inflammatory processes.  On the other hand, a lung abnormality with no increased FDG uptake can be followed for resolution or stability, as false-negative studies are unusual.  The key in this instance should be the opinion of the chest radiologist, on the significance of 'not very brightly'.  Should it be deemed positive or negative?
It is widely believed that lesions that are stable (in size), by chest x-ray or CT over a 2-year period, are highly suggestive of a benign abnormality.  Stability for 6 months is encouraging but should not be interpreted as indicative of a benign lesion.  More recently, a combination of PET and CT images are being performed because some investigators have suggested that the combination of studies will produce even more accurate diagnostic information.  The studies to confirm this hypothesis are currently ongoing.
Reliance on x-ray imaging is not 100% accurate.  The majority of stellate or spiculated lesions are malignant, especially in older individuals who have smoked heavily and this should be weighed in making the decision.  Comparison with previous x-rays could be most helpful and every effort should be made to obtain them.
As stability of this lesion on a CT scan scheduled in June would only be stability for a year, reconsideration should be given to the fine needle biopsy.
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