Bronchioloalveolar carcinoma.

It is helpful to consider BAC as two distinct clinical entities. The solitary or focal form presents as a well circumscribed pulmonary nodule, tends to remain localized with slow growth, and has an excellent prognosis following resection. While it may progress to diffuse disease, this is distinctly unusual and is only supported by Hill's study in the literature. It may metastasize to regional lymph nodes or to distant sites not unlike other carcinomas of the lung, although the incidence of metastatic disease is quite low. The diffuse form of BAC, recognizable as multiple nodules or consolidation, represents an aggressive malignancy with limited survival regardless of intervention.