GRACE :: Lung Cancer

PET Scans for Follow-up of Patients After Surgery or Chemo/Radiation

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We know PET scans can provide additional metabolic information that can be more sensitive and specific for cancer than chest x-rays and even CT scans in the initial staging of lung cancer (see prior post on introduction to PET scans). PET scans are now nearly universally employed in the initial workup, at least of patients who have NSCLC and aren’t already known to have stage IV disease. But how useful is this technology in the setting of surveillance for the patient at risk for recurrent/residual disease after curative treatment?

Unlike CT scans, which are great at discerning shape and size of internal parts of the body, PET scans are metabolic studies that hold the promise of distinguishing between residual viable cancer and non-viable scar tissue after surgery or radiation. A handful of studies in the post-treatment setting show that PET scans have a 96% sensitivity (PET scans identify a problem 96% of the times that there is a problem) and an 84% specificity (there is viable cancer 84% of the time that the PET scan indicates that it’s there) (example references here and here and here). The problem, though, is that unlike the situation of initial staging, where patients haven’t undergone interventions that could cloud the interpretation of a PET scan, except perhaps for a recent biopsy), after surgery or radiation, the inflammatory changes after treatment can also light up on PET scan and make it difficult to interpret what’s cancer and what’s post-treatment inflammation or infection, especially in the vicinity of the original treated cancer. Because of this concern, which is greatest shortly after local treatment, people have generally recommended that PET scans not be pursued until at least 3-6 months after treatment because of the high risk for false positive results (scan shows abnormalities that aren’t really cancer), and also that any areas that appear suspicious on a PET should be confirmed as cancer with CT imaging and a biopsy before pursuing any interventions against presumed cancer. The concept that PET scans will improve our ability to detect curable recurrences or new cancers hasn’t yet been supported by any evidence of better survival or quality of life in patients.

In the face of such a confusing situation, there’s a lot of variability in what oncologists actually do. As a rule, I don’t obtain regular PET scans on patients after curative surgery or chemoradiation, and I’m particularly reluctant to do so in the first few months after completion of treatment. For my patients with a better prognosis, such as stage I and II NSCLC, I routinely obtain CT scans and will order a PET scan if the CT shows something suspicious (typically I’ll get a PET/CT fusion scan 4-6 weeks after the concerning CT to see if the suspicious area has changed and whether it appears as metabolically active on PET). For stage III patients, in whom the risk of recurrence is higher, I do tend to obtain a PET/CT about once per year, otherwise following with CT scans. My general philosophy is that PET scans can be so sensitive but non-specific, especially after chemoradiation with or without surgery for stage III NSCLC, that changes in the absence of CT findings can too often be an anxiety-laden wild goose chase. Chest CT scans provide a lot of detail, so if there isn’t anything suspicious that has emerged from one CT to the next, I’m quite reassured that anything you might find on a PET scan would have a high chance of being a false positive.

This is an area, though, where we’re gaining more experience, and I really hope and expect that we’ll actually get some study results to help guide or practice patterns. In the meantime, it’s the open frontier (the Wild West if you prefer) in terms of using PET scans for surveillance, with people just following their own rules.


8 Responses to PET Scans for Follow-up of Patients After Surgery or Chemo/Radiation

  • ws says:

    First Thanks Dr. West for this site!

    I would love to get your input on the PETS I have received…

    I was a IIIA at diagnosis (4yrs ago) with mets to spine/pelvis 2 yrs later, and cancer free since for the last 2 years. At diagnosis my Pet indicated activity/sub on lung tumor BUT not the 21 positive lymph nodes that were removed when I had surgery.

    I have been getting pet scans every 2 months since the mets to spine (no ct) and an occasional mri of the brain/spine for symptoms. All PET scans have been clear up until about 6 months ago, now every scan reflects growth in my parathyroid and increased suvs (last one 8+).

    I had an ultrasound on the area today. The radiologist/ultrasound tech were unable to locate a nodule and thyroid itself looked normal. The said that there was nothing wrong so no biopsy was done.

    I am currently taking Tarceva for the past 20 months and did remain NED when I was on Iressa for 9 months prior.

    So, 2 questions
    Would you advise continued pet scans as I have been having?
    Why would the thyroid continue to light up? Should the thyroid itself have been biopsied?

    Thanks for your time – Wendy

  • Dr. West says:

    Wendy,

    There is no established role for PET scans in surveillance, and we have remarkably little data on what to do with the information obtained when people do them.

    I would say that what you describe is not the pattern I’d expect to see from metastatic lung cancer.

    I would certainly be curious about what your thyroid blood tests look like, if not a biopsy of the tissue. To me, it sounds like the picture you would expect to see from thyroiditis, but I can’t really provide any more details. I don’t have an expertise in the thyroid, and I think it would be most important to speak with the physician who ordered the scan, and therefore should really manage the follow up of the findings, and/or touch base with a radiologist who has a better knowledge of PET scans.

    -Dr. West

  • mmhu says:

    My husband had a recent Xray, CTscan and ultimatly a PETscan…He has spots on his lungs…He will get a biopsy soon….my question is, Can scar tissue light up under PET scan? He never had a lung infection that he knows of…but he was in Viet Nam and is considered to have been exposed to agent orange and other agents. I know that can cause cancer in the lung. Can it cause scarring in the lung? One of his Viet Nam buddies has had spots on his lungs for a year, has had CTscans every 3 months and the spots have not grown….Is this just wishful thinking??

  • Dr West says:

    An infection or inflammation can be associated with uptake on a PET scan, though typically not as high as most cancers. However, there can definitely be overlap in the lower SUV (standard uptake value) number range, and a PET scan is definitely not conclusive evidence of a cancer. Scarring usually doesn’t have significant uptake associated with it; lesions that are stable over time tend not to be associated with much uptake on a scan.

    -Dr. West

  • mmhu says:

    When reading a PETscan report. Is a SUV max of 4.4 high for the lung tissue? This with no primary lesion visualized.

  • Dr West says:

    It’s in the range that would lead us to be concerned and suspicious, but it’s still ambiguous. There isn’t a threshold “magic number” that indicates cancer vs. another potential cause.

  • drromasa says:

    if the patient is on continuous therapy in case of lymphomas, how often PET scan is recomended? and the protocol of 6-8 weeks gap after chemo/radiotherapy cannot be followed in the continuous therapy.

  • Dr West says:

    Sorry for the delay. We don’t have a lymphoma expert to provide a comment, but you wouldn’t do scans that frequently in this setting. I would say that scans would generally be done every 3-6 months, with them being done less frequently as stability is demonstrated over a longer and longer period of time.

    -Dr. West

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