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Peripheral pulmonary adenocarcinomas with bronchioloalveolar features: immunophenotypes correlate with histologic
J H Ritter1, L D Boucher, M R Wick
1Division of Surgical Pathology, Washington University School of Medicine, St. Louis, Missouri, USA. ritter@path.wustl.edu
Summary
Differentiating primary lung adenocarcinoma from metastases is challenging. This study analyzed keratin markers in peripheral pulmonary adenocarcinomas (PPAs), finding mucinous types resemble gastrointestinal tumors, necessitating careful interpretation of immunohistochemical data.
Area of Science:
- Pulmonary Pathology
- Surgical Pathology
- Oncology
Background:
- Peripheral pulmonary adenocarcinomas (PPAs) can exhibit diverse morphologic patterns, including mucinous and non-mucinous subtypes.
- Distinguishing primary lung adenocarcinomas from metastatic gastrointestinal tumors can be difficult, particularly for mucinous subtypes.
- Previous studies on keratin 7 (K7) and keratin 20 (K20) expression patterns in differentiating these tumors have often lacked precise morphologic classification of PPAs.
Purpose of the Study:
- To evaluate the immunohistochemical expression of K7, K20, and other markers in different morphologic subtypes of peripheral pulmonary adenocarcinomas (PPAs).
- To determine if specific immunophenotypic patterns can reliably differentiate primary PPAs from metastatic enteric adenocarcinomas.
- To assess the utility of K7 and K20 in classifying PPAs based on their histologic features.
Main Methods:
- Thirty-nine cases of primary PPAs were retrospectively reviewed and classified into four groups: Type I (mucinous) bronchioloalveolar carcinoma (BAC1), Type II (nonmucinous) BAC (BAC2), conventional PPA with BAC1-like areas (PPA1), and conventional PPA with BAC2-like foci (PPA2).
- Immunohistochemical staining was performed for K7, K20, carcinoembryonic antigen (CEA), CA19-9, tumor-associated glycoprotein-72 (TAG-72), surfactant apoprotein-A (SPA), and c-erbB-2.
- Clinicopathologic and radiographic data were used to confirm the primary nature of the tumors.
Main Results:
- BAC1 and PPA1 subtypes showed immunophenotypic resemblance to enteric adenocarcinomas, notably lacking surfactant apoprotein-A.
- BAC2 consistently lacked K20 expression, aligning with a Type II pneumocyte origin.
- A subset of PPA2 (28%) demonstrated K20 reactivity, a pattern typically associated with metastatic enteric carcinomas, highlighting diagnostic challenges.
Conclusions:
- Primary mucinous lung tumors (BAC1 and PPA1) can mimic enteric adenocarcinomas immunophenotypically.
- While nonmucinous BAC2 (BAC2) typically lacks K20, some PPA2 subtypes exhibit K20 positivity, complicating differentiation from metastases.
- Immunohistochemical findings in PPAs require careful interpretation within the full clinicopathologic context, as no single marker reliably excludes metastatic enteric disease.