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Bronchoalveolar carcinoma (BAC) is an outdated term historically used to describe a subtype of pulmonary adenocarcinoma with a lepidic growth pattern, i.e., tumor cells spreading along alveolar walls without stromal, vascular, or pleural invasion.

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According to the 2011 IASLC/ATS/ERS classification, BAC has been redefined as:

Old Term	New Classification
BAC	Adenocarcinoma in situ (AIS)
Mixed BAC	Minimally invasive adenocarcinoma (MIA) or Invasive adenocarcinoma, lepidic predominant

Classification

Histologic subtypes (Lepidic Spectrum):

Type	Invasion	Size	Prognosis
Adenocarcinoma in situ (AIS)	None	≤ 3 cm	Excellent (100% cure rate with resection)
Minimally invasive adenocarcinoma (MIA)	≤ 5 mm	≤ 3 cm	Near 100% cure rate
Invasive adenocarcinoma (lepidic predominant)	> 5 mm	Variable	Intermediate prognosis

Clinical Features

Often asymptomatic, detected incidentally. May present with:

Chronic cough
Hemoptysis
Dyspnea (especially in diffuse/multifocal forms)
Copious sputum ("bronchorrhea") in mucinous subtype

Radiology

High-resolution CT (HRCT):

Mucinous types tend to spread via airways (aerogenous spread) → multifocal or bilateral lesions

Pattern	Subtype	Features
Pure ground-glass nodule (GGN)	AIS or MIA	Slow-growing; better prognosis
Part-solid nodule	MIA or invasive	Solid component corresponds to invasive foci
Consolidation with air bronchograms	Mucinous subtype	Mimics pneumonia; may show lobar distribution
Multifocal or diffuse nodules	Invasive mucinous type	Can resemble infiltrative infection or lymphangitic spread
No lymphadenopathy or cavitation	Typical in early AIS	Lymph nodes may appear in advanced or invasive forms

![Axial CT scan with lung windows through the upper lobes in a 79-year-old male with a former 50 pack-year smoking history, having quit 29 years ago. A solitary, ovoid-shaped 16 × 10-mm diameter GGO is visible in the left upper lobe. A tiny, solid component is suggested along the inferior border (arrow). There was no intrathoracic lymphadenopathy. Percutaneous biopsy was suspicious for neoplasm, prompting left upper lobectomy. At histology, this proved to be an adenocarcinoma with mixed infiltrating acinar pattern and more prominent bronchioloalveolar pattern. The central scar measured less than 0.5 cm.

Gandara DR, Aberle D, Lau D, et al. Radiographic Imaging of Bronchioloalveolar Carcinoma: screening, patterns of presentation and response assessment. Journal of Thoracic Oncology. 2006;1(9):S20-S26. doi:10.1016/s1556-0864(15)30005-8](attachment:2f192c2a-a2eb-47c3-a775-f1da813d94ba:image.png)

Axial CT scan with lung windows through the upper lobes in a 79-year-old male with a former 50 pack-year smoking history, having quit 29 years ago. A solitary, ovoid-shaped 16 × 10-mm diameter GGO is visible in the left upper lobe. A tiny, solid component is suggested along the inferior border (arrow). There was no intrathoracic lymphadenopathy. Percutaneous biopsy was suspicious for neoplasm, prompting left upper lobectomy. At histology, this proved to be an adenocarcinoma with mixed infiltrating acinar pattern and more prominent bronchioloalveolar pattern. The central scar measured less than 0.5 cm.