Pneumonic BAC: The Subtype Very Unlike Other Forms of BAC

Howard (Jack) West, MD, Founder and President

One of the issues with BAC is that I've referred to it as potentially very indolent, but as we've learned more about BAC, it's become clear that there is a great degree of heterogeneity in BAC cases. We're learning that the cases that are more often slowly progressing and sometimes exceptionally responsive to EGFR inhibitors like tarceva and iressa are far more likely to be non-mucinous BAC. These typically have the appearance of innumerable small nodules throughout the lungs. There is a form that is the opposite: with sweeping areas of consolidation (also known as opacity) throughout entire areas of lung, typically mucinous, and essentially never responsive to EGFR inhibitors based on what we know right now. This form is called pneumonic BAC, and it is typically very aggressive and unfortunately seems to be resistant to most of our treatments.

It's called pneumonic BAC because it looks for all the world like pneumonia on an x-ray or CT, and I suspect that just about every patient who is ultimately diagnosed with pneumonic BAC is treated for at least weeks and often months with antibiotics. The classic example is that it involves much or sometimes all of a lobe of the lung:

Pneumonic BAC

Because it's mucinous BAC, these patients often describe coughing up large amounts of frothy sputum.

The case above shows involvement in both lungs, so surgery wouldn't generally be performed (although it's sometimes done even palliatively to relieve the productive cough and shortness of breath, since blood runs through this part of the lung and gets no oxygen), but in cases that have involvement of an entire lobe that go to surgery, we sometimes review the cases in a tumor board. Unfortunately, these are cases in which we often see them develop recurrences within months. It's not clear whether chemo leads to a lower risk of recurrence.

As I mentioned above, the limited analysis we've done of mucinous vs. non-mucinous BAC in trials of EGFR inhibitors like iressa and tarceva have shown that responses seem to be essentially limited to the patients with non-mucinous BAC. My colleagues from Memorial Sloan Kettering Cancer Center in NYC have been doing molecular testing on a lot of lung tumors they're treating, and they've told me that these pneumonic BAC cases very often have K-Ras mutations, which goes with a lack of benefit from EGFR inhibitors.

We don't know whether any systemic therapy works for these patients, but I'll describe a clinical case in the next few days that illustrates typical course. In the meantime, the take home message is that while some BAC lesions grow incredibly slowly and are responsive to many treatments, others are very different. I think very few oncologists know the difference, but the pneumonic BAC cases are ones that are typically very aggressive and respond rarely if ever to the oral EGFR inhibitors.



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