What Type of Lung Cancer Is BAC (Bronchioloalveolar Carcinoma)?

As of July 2016, BAC (Bronchioloalveolar carcinoma) is a term which is no longer in use but was used between 2004 and 2011 to define a particular subtype of lung adenocarcinoma. That said, some oncologists still use this term, so the history and characteristics of what was once classified as BAC will be described here.

BAC, when it was classified under this heading, had sometimes been called the “mystery” lung cancer. Accounting for 2 to 14 percent of all lung cancers, less was known about this type of cancer than other non-small cell lung cancers. 

As noted above, BAC has now been reclassified under the heading of lung adenocarcinomas, but since this term is sometimes still used by clinicians, it will be described in that setting. In the new classification, BAC may be referred to as "lepidic predominant adenocarcinoma" based on the typical growth pattern of the tumor. BAC develops in cells near in the small air sacs (alveoli) in the outer regions of the lungs. It spreads either along the tissue that separates the alveoli or through the airways. Unlike other forms of lung cancer that often spread to the lining of the lungs (the pleura) and other regions of the body, BAC spreads primarily within the lungs. It can appear as a single spot in the periphery of the lungs, or as scattered spots throughout the lungs. There are 2 main types of BAC: non-mucinous BAC is more common and found more often in smokers, and mucinous BAC, which is less common and often found in non-smokers.

How Does It Differ From Other Lung Cancers?

BAC is more likely to affect non-smokers, women, and Asians (especially eastern Asians) than other forms of lung cancer. Its incidence appears to be increasing, especially among younger non-smoking women.

Symptoms of BAC are similar to symptoms seen with other lung cancers, and include a persistent cough, coughing up blood (hemoptysis), and chest pain. But it has also been called the “masquerader.” It is not uncommon for BAC to be mistaken for pneumonia or other lung diseases before it is diagnosed.

BAC diagnosis is also similar to the diagnosis of other lung cancers, with a few exceptions. A diagnosis of BAC requires a sample of tissue, and fine-needle aspiration biopsy can provide the diagnosis roughly half the time. Unlike other lung cancers, where PET scans are helpful in addition to CT scans in determining where cancer is present, PET scans are less reliable. Staging (stages 1 to 4 or TNM staging) is similar to staging other forms of lung cancer.

Surgery is the treatment of choice for BAC, and when a single tumor can be removed, there is often a good chance that it will be cured. It appears to be less sensitive to traditional chemotherapy, and there is controversy over whether or not adjuvant chemotherapy (chemotherapy given along with surgery) should be used with surgery. BAC does appear to be more sensitive to the newer targeted therapies, treatments designed to target specific gene mutations within the tumor.  People with this type of lung cancer should have genetic testing (molecular profiling) done on their tumor. There are now treatments approved for these lung cancers which have EGFR mutations, ALK rearrangements , and ROS1 rearrangements, with medications being used in clinical trials for those with other genetic changes in their tumors as well.

Lung transplants are being looked at as an additional treatment, and if the cancer does not recur in the transplanted lungs, it offers another chance for long-term survival.

In general, the survival rate is significantly better for BAC than for other forms of non-small cell lung cancer, especially when it is caught early and only one tumor is present. In one study, those who were diagnosed with BAC and had tumors less than 3 centimeters in diameter, had a 5-year survival rate of 100 percent with surgery. With later stages of the disease survival rates vary considerably, depending on factors such as separate tumors in the same lobe, lymph node involvement, and distant spread of the tumor.