lepidic pulmonary adenocarcinoma

Definition: In the 2004, WHO classification, the term "bronchioloalveolar carcinoma" (BAC) is restricted to tumors in which the characteristic lepidic growth pattern (growth along intact alveolar septae) comprises the entire tumor.

BAC therefore lacks any stromal, pleural, or lymphatic invasion, although fibrous tissue or a chronic inflammatory cell infiltrate may thicken the alveolar septa. Both mucinous and non-mucinous subtypes are recognized. In the 2011 classification scheme, these tumors have been renamed as " pulmonary adenocarcinoma in situ " or " lepdidic adenocarcinoma ".

Historically, pulmonary adenocarcinomas with lepidic growth (growth along alveolar septa) have been termed bronchioloalveolar carcinoma (BAC), a term coined by Dr Averill Liebow in 1960. He noted that BAC had an indolent clinical course compared to other aggressive types of lung cancer.

The definition of BAC was made more stringent over the years and was eventually defined as a tumor showing " entirely lepidic growth without any tumoral invasion of the stroma or chorion ".

Minimal invasion or limited invasion

Subsequent studies focused on small lepidic-predominant tumors with limited areas of invasion, which have shown that the size of invasion or scarring may be more prognostic than gross tumor size.

Tumors with less than or equal to 5 mm of invasion are associated with excellent survival and have been termed minimally invasive adenocarcinoma (MIA).

A consensus classification was proposed by the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society in 2011, which has been adopted by the 2015 World Health Organization (WHO) classification of pulmonary adenocarcinoma.

This classification abandons the term BAC in favor of adenocarcinoma in situ (AIS) and formally introduces MIA as a diagnostic category, whereas tumors with greater than 5 mm invasion are classified as invasive adenocarcinoma (IA).

AIS and MIA are limited to tumors less than or equal to 3 cm because data on larger tumors are very limited.

Studies have shown that solid and micropapillary tumors are more aggressive, whereas lepidic tumors have better survival, so it is also recommended that IAs be subclassified according to the predominant histologic pattern.

Digital cases

 JRC:1596 : Bronchioloalveolar carcinoma.
 JRC:6163 : Bronchioloalveolar carcinoma.
 JRC:6170 : Bronchioloalveolar carcinoma.
 JRC:6171 : Bronchioloalveolar carcinoma.
 JRC:6173 : Bronchioloalveolar carcinoma.
 JRC:6174 : Bronchioloalveolar carcinoma.
 JRC:19397 : Bronchioloalveolar carcinoma (?) or acinar adenocarcinoma.

Macroscopy

 The tumors are typically peripherally located.
 It is light tan and is composed of multiple diffuse nodules coalescing producing a "bronchopneumonia"-like consolidation grossly (these tumors may be confused with bronchopneumonia grossly).
 Localized tumor mass: Usually @<@ 3 cm in diameter.
 Multinodular pattern: Extensive areas of lung parenchyma are involved in miliary fashion.
 Diffuse pattern: No distinct tumor mass or nodule is present.
 Lung parenchyma appears congested, mimicking lobar pneumonia.

 Predominant Pattern/Injury Type

• Circumscribed
• Mucinous
• Diffuse

Microscopy

 Malignant glandular epithelial cells growing along alveolar walls in a lepidic pattern.
 Nuclei of cells are hyperchromatic.
 Conventional type

• Tumor cells are small and dark with hyperchromatic nuclei and scant cytoplasm
• Tumor cells display prominent hobnail appearance and are devoid of nucleoli or mitotic figures

 Mucinous type

• Tumor cells are tall columnar and contain abundant mucinous cytoplasm

Types

 mucinous type bronchioloalveolar carcinoma
 non-mucinous type bronchioloalveolar carcinoma

Differential diagnosis

 Atypical Adenomatous Hyperplasia (AAH)

• Tumor nodule @<@ 0.5 cm in greatest dimension
• Histology very similar to BAC

 Metastatic Adenocarcinoma

• Past or present history of adenocarcinoma outside of thoracic cavity
• Immunohistochemical studies may be helpful in determining primary site

 Pulmonary Invasive Adenocarcinoma

• BAC lacks presence of vascular, lymphatic, pleural, or interstitial involvement by tumor cells

Checklist

 Clinically Relevant Pathologic Features

• Noninvasive pattern
• Diagnosis of BAC cannot be achieved in biopsy specimens
• Histopathological examination of entire tumor is required for diagnosis of BAC
• Lymph node sampling is required to properly rule out metastatic disease

 Pathologic Interpretation Pearls

• Extensive pools of mucin
• Alveolar wall lined by neoplastic cells
• Absence of pleural invasion
• Absence of interstitial invasion

See also

 pulmonary adenocarcinoma

References

 Benjamin DR, Cahill JL. Bronchioloalveolar carcinoma of the lung and congenital cystic adenomatoid malformation. Am J Clin Pathol 1991; 95:889-92.

 Hajdu SI: The story of bronchioloalveolar carcinoma. Ann Clin Lab Sci. 35(3):336-8, 2005

 Travis WD et al: Tumours of the lung, pleura, thymus, and heart. Pathology & Genetics: World Health Organization (WHO). Lyon: IARC Press. 38, 2004

 Sidhu GS et al: The concept of bronchioloalveolar cell adenocarcinoma: redefinition, a critique of the 1999 WHO classification, and an ultrastructural analysis of 155 cases. Int J Surg Pathol. 11(2):89-99, 2003

 Colby TV et al: Tumors of the lower respiratory tract. Atlas of Tumor Pathology: Armed Forces Institute of Pathology (AFIP). (13):203, 1995

 Daly RC et al: Bronchoalveolar carcinoma: factors affecting survival. Ann Thorac Surg. 51(3):368-76; discussion 376-7, 1991

 Manning JT Jr et al: Bronchioloalveolar carcinoma: The significance of two histopathologic types. Cancer. 54(3):525-34, 1984

 Carter D et al: Tumors of the lower respiratory tract. Armed Forces Institute of Pathology (AFIP). (17):127, 1980

 Liebow AA: Bronchiolo-alveolar carcinoma. Adv Intern Med. 10:329-58, 1960