Bronchioloalveolar Carcinoma - Classification

Classification

Lung cancers are an extremely heterogeneous family of malignant neoplasms, with well over 50 different histological variants recognized under the 2004 revision of the World Health Organization ("WHO-2004") typing system, currently the most widely used lung cancer classification scheme. Because these variants can have widely differing genetic, biological, and clinical properties, including response to treatment, correct classification of lung cancer cases are necessary to assure that lung cancer patients receive optimum management.

Approximately 98% of lung cancers are carcinoma, which are tumors composed of cells with epithelial characteristics. 8 major groups of lung carcinomas are recognized in WHO-2004:

• Squamous Cell Carcinoma
• Small Cell Carcinoma
• Adenocarcinoma
• Large Cell Carcinoma
• Adenosquamous Carcinoma
• Sarcomatoid Carcinoma
• Carcinoid Tumor
• Salivary Gland-like Carcinoma

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.