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Bronchioloalveolar Carcinoma (BAC)

Myths and Misconceptions About Bronchioloalveolar Carcinoma (BAC)

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GCVL_LU-AA02_Myths and Misconceptions About Bronchioloalveolar Carcinoma (BAC)

Unfortunately, there is as much misinformation as good information about the unusual subtype of lung cancer known as bronchioloalveolar carcinoma (BAC) or adenocarcinoma in situ. Dr. Jack West reviews the top 5 myths.

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Bronchioloalveolar Carcinoma (BAC): What is It?

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GRACE Cancer Video Library - Lung

GCVL_LU-AA01_Bronchioloalveolar Carcinoma (BAC): What is It?

Bronchioloalveolar carcinoma (BAC), also known as adenocarcinoma in situ, is an unusual subtype of lung cancer with its own appearance under a microscope and on imaging. Dr. Jack West introduces some of the basics of the unique features of BAC.

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Treating Bronchioloalveolar Carcinoma by Not Over-Treating It: What the Experts Really Do (and Don’t Do)

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I’m completing a chapter in a key lung cancer textbook on managing multi-focal bronchioloalveolar carcinoma, a clinical entity that is in the process of being re-labeled lepidic predominant adenocarcinoma (LPA) (lepidic meaning scale-like, which is the classic way that the cells are defined as spreading when looked at under a microscope). I suspect that it will continue to be called multifocal or advanced BAC for a long time (after all, the formal staging of small cell lung cancer goes from stages 1 to 4, but nobody ever uses that, classifying it as just limited or extensive stage).  

When asked to write this chapter, I faced the challenge of there being very little actual hard data on managing multifocal BAC.  Though many experts have a very similar approach, this is actually based on expertise, good judgment, and clinical experience more than data we can point to, and I don’t think this approach has ever been articulated in a scientific paper or book chapter, so I’m hoping this will be a valuable addition to the literature.

As I reviewed the papers out there, what struck me most are two things: 

1) There is incredible variability in the appearance and clinical behavior of what is called advanced BAC in the clinical world — some of it is aggressive and imminently threatening, and much of it is very slow growing and among the least threatening cases ever labeled as lung cancer.

2) People with a very slow growth rate are likely to do very, very well no matter what treatments they get, as much despite as because of those treatments.  In many cases, interventions are pursued on patients who are destined to do very well, and then when their short term survival is good, the people who did that intervention write a paper saying how their approach is feasible and attractive because the patients did well — not recognizing, or at least glossing over the idea, that they were going to do very well anyway.

I would say that in no other area of lung cancer care is it more important to distinguish between what can be done and what should be done.  And the real experts know when to not intervene.

So here is the algorithm I developed, which isn’t beautiful, but you can see that it focuses on seeing what is actually changing rather than treating reflexively based on a label on a pathology report or single a scan finding.  Essentially, it says to try to avoid intervening at all unless or until you see clinically significant change (which I would consider as something that is readily apparent as progression on scans done 6 months apart or less), and then if you see progression, clarify whether it’s limited to one lesion or progressing more diffusely in multiple areas.

Multifocal BAC algorithm

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How does the diagnosis of BAC shape systemic therapy considerations today?

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It’s not uncommon for a question here to be about the a pathologist’s terminology on a report that equivocates about whether a lesion is bronchioloalveolar carcinoma (BAC) or another form of adenocarcinoma, perhaps “well-differentiated adenocarcinoma”, especially if it has a radiographic appearance of a hazy infiltrate or many small ground glass opacities. Meanwhile, there’s a new classification of lung cancer subtypes that obliterates the term BAC, instead favoring a definition of adenocarcinoma in situ, classifying small non-invasive lesions previously called BAC as a pre-malignant condition. How have the changes over the past few years changed how we should approach BAC?

I would have to say that the new reassignment of BAC as adenocarcinoma in situ hasn’t taken the lung cancer world by storm and that I still think of the clinical entity as BAC. For the preceding decade, the definition the pathologist’s used technically excluded a lesion with even 1% or 5% of the lesion being invasive as being called BAC, even if it acted for all the world like BAC. Clinicians learned not to be too hung up on a pathologist’s technical definitions and tended to define BAC more functionally/operationally. General oncologists and expert lung cancer specialists alike managed BAC based on the overall picture of how it behaved if it looked like a BAC pattern.

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Basics of Bronchioloalveolar Carcinoma (BAC)

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Bronchioloalveolar carcinoma, or BAC, is a unique subtype of non-small cell lung cancer (NSCLC) that has unique features in terms of the demographics of who gets it, how it appears on scans, how it often behaves, and potentially in how it responds to treatment. It is a subset of lung cancer for which most of what we know emerged in the last 10 years, with our understanding of this entity, and even the definition of BAC, still evolving.

What is BAC?

BAC was first identified and defined as a separate subtype of lung cancer by Dr. Averill Liebow in 1960. At that time, he highlighted it as a form of well differentiated adenocarcinoma of the lung that appeared to not be able to invade the surrounding lung scaffolding and spread within the lung(s), presumably aerogenously and/or through lymphatic channels.

bac-under-microscope-and-on-cxr1 (click on image to enlarge)

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