PET scans are an important way to discriminate between metabolically active nodules, suggestive of cancer but sometimes representing inflammation or infection, and non-PET-avid lesions that are felt much likely to represent cancer. They are also a cornerstone of “clinical” staging by imaging and patient exam (vs. “pathologic” staging by surgery to clarify where cancer is or isn’t). PET scans, however, require rapid metabolic activity to highlight a cancer, so there’s good reason to question whether PET scans can be used effectively for the BAC subset of lung cancers, which, as I’ve described in prior posts (here, for instance), can be remarkably indolent.
No specific prospective (planned ahead of time) studies of PET scanning in BAC have ever been done, but there are now enough BAC patients in other trials for us to look retrospectively at meaningful numbers, so we can now begin to assess the feasibility of PET scans for diagnosis and staging of BAC.
By way of background, one key study demonstrated that PET scans for lung cancerhad a sensitivity of 97% (meaning 97% of lung cancers would be found to be abnormal on a PET scan), and a specificity of 78% (so 78% of the time, the abnormality would be from cancer and not another source, like infection or inflammation) (abstract here). Breaking out 7 BAC patients from a 29 patients (and 30 total lung adenocarcinomas), Higashi and colleagues from Japan (abstract here) found that only 3 of the 7 registered positive results on the PET scan. In contrast, only one of the other 23 non-BAC adenocarcinomas remained undetected on PET scans. This same study also reported that there is a stepwise increase in the mean (bascially the average) standard uptake value (SUV, the measure of metabolic intensity on a PET scan) from BAC tumors (mean SUV 1.36), to well-differentiated adenocarcinomas (mean SUV) to moderately differentiated adenocarcinomas (mean SUV 4.63). Heyneman and colleagues (abstract here) reviewed their results from a tumor registry over a 6-year period, during which time they identified 15 patients who had a proven BAC lesion and had also undergone a PET scan. Of these, nine were considered positive. In particular, focal BAC was more likely to lead to a false negative PET scan than the more widespread pneumonic form (in which most or all of an entire lung lobe is full of BAC).
Continuing along this theme, a Korean trial by Kim & colleagues (abstract here) reported on 9 BAC patients among 48 with lung cancer. In this population, the mean SUV was significantly lower among the BAC patients compared with those who had a non-BAC lung cancer.
(Click on image to enlarge)
Based on these results, the authors argued that BAC there is a problematic risk for false negative results (a study reported as negative but actually really having the disease) on PET scanning.
Overall, the results do suggest that while BAC can sometimes be identified on a PET scan, these cancers are disproportionately over-represented among the lung cancers that remain PET negative. Because of this, negative PET scan results should not be interpreted as ruling out cancer in people with CT findings suggestive of a BAC picture. Instead, this is a setting where we can’t be reassured and need additional studies, potentially follow-up imaging or a biopsy, to clarify what’s going on.
posted by Dr. West @ 8:53 pm link to this post
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October 22nd, 2007 at 7:26 am
Hi Dr. West:
Thank you for the article about BAC - I, of course, have a personal interest in this rare process and I always so appreciate your articles on it.
As you know I went to a Vancouver private PET scanning clinic to get my PET done which did turn out to be BAC. I am not certain; however, I believe that had I not had the CT scan showing an area of concern prior to receiving the PET scan that I would have been in the percentage of having a false negative. My SUV reading was 1.4; however, on the PET scan they do say it is highly suspicious for carcinoid/bac lesion. I emphatically agree that it is beneficial to have the 2 tests used together for a better diagnosis and not rely totally on the SUV readings.
Personally, I believe the radiologist at the PET centre had the benefit of knowing the appearance of the lesion/the increased growth over a 3 month period, etc. which helped him suggest a diagnosis based on the previous information submitted - not just the SUV. Had they just gone by the SUV reading alone I would have been told not to worry and just go home.
In my case I wanted the PET to let me know if it had metastized as I did not want to do the roller coaster ride of being booked for surgery only to have it cancelled if they were unable to perform surgery. The PET gave me piece of mind and I truly don’t think I can put a price on that. It also enabled my surgery to be performed in a timely manner (from diagnosis to surgery-1 month) as the surgeon pretty much knew what he was dealing with. I think PET scans are a wonderful tool; however, as you said in the case of BAC I believe they can only be used as an additional test, not the only test.
Enjoy your Monday - we are still snow free here in Alberta - can it remain that way until Christmas - I highly doubt it!
Linda
October 22nd, 2007 at 2:06 pm
Dr. West:
I am always interested, for obvious reasons, in comparing pure BAC with Adenocarcinoma with BAC features. After reading your piece on BAC & PET I wondered if there are similar studies for Adenocarcinoma with BAC features and PET’s SUV.
I only found a short piece of news from the Elsevier Global Medical News from October 19 2007, link here http://www.oncologystat.com/home/news
/PET-CT_Combination_Distinguishes_
Bronchoalveolar_Carcinoma.html?null) where they describe a study from Johns Hopkins U. on 6 patients with pure BAC, 8 with ADWBAC out of a database of 630 cases. interestingly, they got a mean max SUV for pure BAC of 2.74 vs 8.93(!) for ADWBAC. This seems to suggest that ADWBAC tends to be much more metabolically active than pure BAC. Also The SUV max for pure BAC are much higher than the number from the Japanese study that you mention.
Do you know of similar studies of ADWBAC and PET?
Thanks
Carlos
October 22nd, 2007 at 8:56 pm
Carlos,
Adenocarcinoma with BAC features would usually be classified just as adenocarcinoma. There’s a huge amount in the literature about standard invasive adenocarcinoma, including much of the comparison to BAC noted in the post above. Basically, I don’t think there’s much literature specifically on this, but I would say that the continuum from pure BAC to BAC with focal invasion to adenocarcinoma with BAC features and then just plain invasive adenocarcinoma would show increasing SUV results as you move up the spectrum.
-Dr. West