Adenocarcinoma in situ of the lung
| Bronchioloalveolar carcinoma | |
|---|---|
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| Detail of a CT thorax showing pseudonodules with ground glass pattern consistent with bronchioloalveolar carcinoma | |
| Classification and external resources | |
| Specialty | oncology |
| ICD-10 | C34 |
| ICD-9-CM | 162 |
| ICD-O | M8250/3 |
| MeSH | D002282 |
In situ pulmonary adenocarcinoma (AIS), previously called "Bronchioloalveolar carcinoma" (BAC), is a term describing certain variants of lung cancer arising in the distal bronchioles or alveoli that initially exhibit a specific non-invasive growth pattern. BAC is a type of non-small-cell lung cancer (NSCLC). AIS is defined as a small (≤3 cm) solitary tumour with pure alveolar epithelial appearance (lepidic growth), lacking any invasion of the interstitium. If completely resected, the prognosis of surgically treated AIS is 100%.
In WHO-2004, BACs are one of four specific histologic subtypes of lung adenocarcinoma, along with acinar adenocarcinoma, papillary adenocarcinoma, and solid adenocarcinoma with mucin production. However, approximately 80% of adenocarcinomas are found to contain two (or more) of these four subtypes. Multiphasic tumors such as these are classified into a fifth "subtype", termed adenocarcinoma with mixed subtypes.
There are other classification systems that have been proposed for lung cancers, including BACs and other forms of adenocarcinoma. The Noguchi classification system for small adenocarcinomas has received considerable attention, particularly in Japan, but has not been nearly as widely applied and recognized as the WHO system.
Like other forms of lung carcinoma, BAC possesses unique clinical and pathological features, prognosis, and responses to different treatments.
BAC occurs in two major histopathological variants, mucinous BAC (m-BAC, 20–25% of cases) and non mucinous BAC (nm-BAC, 75–80% of cases). Very rarely, BAC can also occur as a "mixed mucinous and non-mucinous" (or "indeterminant") variant.
Nonmucinous BAC is thought to derive from a transformed cell in the distal airways and terminal respiratory units, and often shows features of club cell or Type II pneumocyte differentiation. Mucinous BAC, in contrast, probably derives from a transformed glandular cell in distal bronchioles.
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