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The new USPSTF lung cancer screening guidelines are about to produce an enormous wave of abnormal chest CTs, with suspicious pulmonary nodules in millions of current and former U.S. smokers. Many will be surgically removed, and thousands of people will be saved from premature death from lung cancer. That's great news -- mostly.
Less widely reported is that up to 18% of these early-detected lung cancers will be so slow-growing as to be effectively harmless -- cases of lung cancer overdiagnosis that would have been best left undetected. Most of these nonaggressive, noninvasive lung cancers have a subsolid or "ground glass" appearance on chest CT. Many are adenocarcinoma in situ, the cancer formerly known as bronchoalveolar (or bronchioloalveolar) carcinoma.
Because it's impossible to accurately predict a lung cancer's future behavior (and because the idea of "harmless" lung cancers is still a pretty foreign concept, even to pulmonologists and oncologists), patients with ground glass tumors are usually referred for curative lung resection surgery. Traditional surgery for lung cancer has been to remove the entire lobe containing the cancer (lobectomy) -- about half of one lung -- which can cause significant loss in exercise ability, especially for someone already impaired by lung disease such as COPD. Those with harmless lesions experience avoidable risk both from the surgery itself, and from the resulting loss of lung function.
That's why it's good news that in the January 2014 issue of Chest, Yasuhiro Tsutani, Yoshihiro Miyata, Morihito Okada et al report that less-radical surgery produces survival rates as good as traditional lobecotmy for stage IA subsolid lung cancer, in a medium-sized series.
What They Did
Authors retrospectively analyzed 239 consecutive patients undergoing complete resection of stage IA ground glass / subsolid adenocarcinoma of the lung at 4 institutions in Japan.
What They Found
There was no difference in 3 year recurrence free survival between patients undergoing lobectomies vs. sublobar resections for stage IA lung cancer with subsolid component:
- Patients who received lobectomies (n=90): 96% 3-year recurrence-free survival;
- Segmentectomies (n=56): 96%
- Wedge resection (n=93): 98%
For those with T1b subtypes (>2cm), the numbers for 3 year recurrence free survival were:
- Lobectomy (n=51): 94%
- Segmentectomy (n=19): 93%
- Wedge resection (n=14): 100%
However, 2 of 84 patients with T1b tumors had lymph node metastases. A segmentectomy is more likely to excise lymph node metastases than a wedge resection.
Authors report their multivariate analysis showed that tumor size, maximum standardized uptake value on 18F-fluorodeoxyglucose PET/CT scan, and surgical procedure did not affect survival in these ground glass lung cancers.
What It Means
These aren't big numbers, and a larger prospective observational case series, or even a randomized trial, would be needed to conclude anything definitively.
But there is every reason to believe that sublobar resections can "cure" early ground-glass/subsolid adenocarcinomas just as well as lobectomies can and produce long-term survival numbers well into the 90+ percentile. That's partly because although many people were truly cured of lethal cancers in this study, most likely, a significant proportion didn't need surgery in the first place. This is a form of overdiagnosis bias in survival statistics.
In a sample of harmless cancers, the 3-year recurrence-free survival is 100%, whether surgery is done or not. The higher the proportion of indolent cancers, the higher the survival rates, regardless of the intervention. Thyroid cancer (which also frequently presents in harmless/indolent form) is the prototypical example, with a near-100% 5-year survival rate after thyroidectomy (and without it, probably nearly that). Recent evidence suggests breast cancer is subject to the same principle, which is likely operating here -- but to what degree can't be known.
Until we have a better way of identifying which ground glass / subsolid lung cancers are truly indolent, I'm certainly not going to recommend wholesale observation over surgery. Instead, I'll dutifully and guiltily refer almost everyone who's a "good surgical candidate" for resections, knowing full well that some of them don't need them -- that the well-intentioned surgery is actually harmful. What's encouraging about this study is that (if replicated on a larger scale, or just believed by thoracic surgeons) it could lead to less-disabling surgeries for the large numbers of people who are about to be diagnosed with early lung cancer -- some of whom would have been better off not finding out.
Yasuhiro Tsutani et al. Appropriate Sublobar Resection Choice for Ground Glass Opacity-Dominant Clinical Stage IA Lung Adenocarcinoma:Wedge Resection or Segmentectomy. Chest. 2014;145(1):66-71. doi:10.1378/chest.13-1094