To answer Dr. Pennell’s question, I do think that a disproportionate amount of what we see in screening efforts is and will be BAC/AIS. This is part of the controversy in screening: we tend to find more indolent, potentially clinically insignificant (or at least less threatening) disease than the cross-section we see now.

For Linda’s question, these changes are made by pathologists who have never managed patient with cancer, so the changes in clinical practice will most definitely be left to the clinicians. I had already been inclined to follow my patients with non-invasive BAC on a less frequent interval for scans and follow-up, knowing from my experience with the disease that its pace was definitely slower than other NSCLC, but this really provides some additional justification. Most significantly, it will highlight that patients with a 1 cm non-invasive, non-mucinous BAC have an extremely favorable prognosis, as do those with just a tiny focus of invasiveness. The implication is that the non-invasive form leads to the invasive component, but I wouldn’t go so far as to say that this causal link has been established.

-Dr. West

It refers to the measurement of the lesion as it appears under the microscope. I am not 100% sure how this system would apply for multiple nodules, which should increase the stage and make the interpretation less clear. To me, these results are most applicable to small (2 cm or less) BAC-type lesions, since the presumption is that lesions larger than 2 cm are more likely to have some area of invasiveness and cannot be as easily presumed to have an exceptionally favorable prognosis, as suggested by the term “adenocarcinoma in situ”, which is consistent with a pre-cancerous disease. As I said, I don’t think this system is as clearly applicable to multifocal disease, but I’m going to contact one of the experts involved with this proposal and see what I can find out.

The general idea is that when we see ground-glass opacities (GGOs), those correspond to the non-invasive component of “pure BAC” that would now be called AIS. Often, what you’ll see on a scan is a GGO with a solid area in the middle or adjacent, and this often represents an invasive area. So now a 3 mm solid area along one edge of a GGO that measures 9 mm might be resected and be shown to actually be 3 mm of invasive carcinoma and the rest being AIS. This would now be a “minimally invasive adenocarcinoma” (MIA).

However, even with these general correlations of scan results with microscopic findings, we definitely aren’t great predictors of what a subcentimeter nodule or opacity represents and would typically follow the general approach of following a small, ambiguous lesion while looking for growth, then biopsying.

A very significant proportion of the lung cancers we find in screening studies are either what would be considered AIS or MIA. In fact, one of the nagging questions about screening is whether a disproportionate number of lung cancers detected fall on the most indolent end of the lung cancer spectrum, as these AIS or MIAs.