Bronchioloalveolar Carcinoma Lung Cancer

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As of July 2016, BAC (bronchioloalveolar carcinoma) is a term that 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.

Bronchioloalveolar carcinoma of the lungs (BAC), as noted above, has now been reclassified as a form of lung adenocarcinoma. That said, research on BAC can still be helpful in describing this particular type of tumor, and some oncologists may still use the term. In the past, when BAC was used as a classification of lung cancer, this type of cancer was thought to account for 2% to 14% of all lung cancers, though less was known about this type of non-small cell lung cancer. For this reason and more, BAC (and now the subtype of lung adenocarcinoma to which it has been reclassified) has been referred to as the "mystery of lung cancer."

An understanding of these tumors is particularly important, as the incidence is increasing (especially in young women who have never smoked) in contrast to the general decline in lung cancer cases. We will look at the characteristics of these tumors, symptoms, causes and risk factors, prognosis, and how they are diagnosed and treated.

Classification and Characteristics of BAC

Since the term bronchioloalveolar carcinoma (BAC) is still used, most of what is described here will be done in the context of the older diagnosis.

In the new classification, BAC may be referred to as "lepidic predominant adenocarcinoma" based on the typical growth pattern of the tumor. 

Bronchioloalveolar carcinomas may appear as a single spot in the periphery of the lungs, or as scattered spots throughout one or both lungs.

There are two 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 BAC Differs From Other Lung Cancers

It's well known that bronchioloalveolar differs from many other lung cancers both in the population that develops these tumors, and the behavior of the tumors themselves.

BAC is more likely to affect never-smokers, women, young adults, and Asians (especially eastern Asians) than other forms of lung cancer. The incidence of non-small cell lung cancer in never smokers, especially young women who have never smoked, appears to be primarily an increase in these tumors previously known as BAC.

BAC develops in cells in the small air sacs (alveoli) in the outer regions (periphery) of the lungs. It spreads either along the tissue that separates the alveoli or through the airways. (This spread through the airways (aerogenous spread) appears to be unique to lung cancer, and especially to this form of lung adenocarcinoma).

Unlike other forms of lung cancer that often spread to the lining of the lungs (the pleura) and other regions of the body such as the liver, brain, and adrenal glands, BAC spreads primarily within the lungs.

Signs and Symptoms

Symptoms of BAC can be similar to symptoms seen with other lung cancers and include a persistent cough, coughing up blood (hemoptysis), and chest pain. Since they are located in the outer regions of the lungs away from the airways, however, these "typical symptoms" may be less common, and symptoms such as shortness of breath with exertion or profound fatigue may first be noted.

BAC 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, sometimes for an extended period of time.

Since BAC tends to spread within the lungs more often than to distant regions, symptoms related to the spread of lung cancer (such as headaches due to brain metastases) are less common.

Diagnosis

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 for other forms of lung cancer.

Treatments

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 that 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.

Prognosis

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.

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