Bronchioloalveolar Carcinoma

Until recently, bronchioalveolar carcinoma (BAC) encompassed various premalignant lesions of pulmonary adenocarcinoma that develops from the epithelium of the terminal bronchioles and their acini at the peripheries of the lung and was distinguished by the absence of blood vessel or pleural involvement (also known as lepidic growth) [1] [2]. Because of its poor histological and radiographic specificity, bronchioalveolar carcinoma was recently replaced with the terms pulmonary adenocarcinoma in situ (AIS) and minimally invasive adenocarcinoma (MIA), with mucinous, non-mucinous and mixed forms as subtypes of both lesions [2] [3] [4] [5] [6]. In addition, subtypes of invasive adenocarcinoma (lepidic predominant adenocarcinoma - LPA, and invasive mucinous adenocarcinoma) are also terms that have arisen from BAC [3]. One of the most important features of BAC is that its clinical presentation, comprised of a cough, chest pain and the production of sputum, can have a broad differential diagnosis (infections, hypersensitivity pneumonitis, etc.) [1]. The absence of fever, however, which is never seen in BAC, should point toward a noninfectious etiology [1]. Unfortunately, more than 60% of patients have no apparent symptoms, thus the diagnosis might be difficult to make [1]. But because BAC is a premalignant lesion and because 5-year survival rates are 100% if appropriate therapy is implemented early on, usually in the form of surgical resection, recognition of these lesions is vital in limiting its progression to a malignant tumor, which then carries a significantly poor prognosis regardless of the stage [6] [7].

Premalignant lesions of the lungs can only be detected with a comprehensive approach, starting with a detailed patient history and a complete physical examination that could possibly identify an ongoing pathological process in the lungs. As signs and symptoms are often lacking, however, imaging studies, a full laboratory workup, and pathohistological evaluation are necessary steps. The absence of leukocytosis in the presence of respiratory symptoms can often exclude pneumonia and other infectious processes [1]. Conversely, the use of imaging procedures provides essential clues in making a presumptive diagnosis [1]. Recent reports have established that BAC (or all of its newly described variants) appears as a solitary nodule ranging from 5-30 mm in diameter, although lobar, multilobar or even patchy infiltrates may be seen on plain radiography or computed tomography (CT), suggesting its multicentric development in some patients [1] [3] [5] [6]. CT is often preferred to chest X-rays, as it provides a better view of the lung parenchyma, but a biopsy of the lesion is often necessary, especially when inconclusive findings are seen on CT [5]. Thus, the diagnosis of BAC (now called AIS or MIA) now rests on radiographic criteria, but more importantly, on a proper histopathological examination [5] [6].

1. Thompson WH. Bronchioloalveolar carcinoma masquerading as pneumonia. Respir Care. 2004 Nov;49(11):1349-53.
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7. Jiang L, Yin W, Peng G, et al. Prognosis and status of lymph node involvement in patients with adenocarcinoma in situ and minimally invasive adenocarcinoma—a systematic literature review and pooled-data analysis. J Thorac Dis. 2015;7(11):2003-2009.