Immunohistochemical evaluation of inhibin-alpha in non-small-cell lung carcinomas--a pitfall in diagnosing metastatic pulmonary carcinomas.

CONTEXT

Inhibin-alpha is commonly used in differentiating non-small-cell lung carcinoma from certain metastatic carcinomas, but a study on a large series of primary lung cancer cases has not yet been published.

OBJECTIVE

To establish whether non-small-cell lung carcinoma can express inhibin-alpha; if so, caution should be exercised when using the molecule to evaluate metastatic lung cancer in both lung and extrapulmonary sites.

DESIGN

187 cases of non-small-cell lung carcinoma and small-cell lung carcinoma were evaluated for expression of inhibin-alpha on both routine and tissue microarray sections by immunohistochemistry. These cases included 90 mixed or acinar adenocarcinomas, 2 acinar carcinomas with mucinous feature, 6 bronchioloalveolar carcinomas, 9 large-cell carcinomas, 2 adenosquamous carcinomas, 2 sarcomatoid carcinomas, 41 squamous cell carcinomas, 12 typical carcinoid tumors, 3 atypical carcinoid tumors, 20 small-cell lung carcinomas, and 19 cases of normal lung. The staining intensity was graded as weak, intermediate, or strong. The distribution was recorded as negative (no staining), 1+ (<25%), 2+ (26-50%), 3+ (51-75%), or 4+ (>75%). Cytoplasmic coarse granular staining for inhibin-alpha was the indicator for a positive result.

RESULTS

A subset of primary mixed or acinar and mucin-producing acinar carcinomas (10%) and large-cell carcinomas (22%) expressed inhibin-alpha. No expression of inhibin alpha was observed in the remaining cancers or normal lung samples.

CONCLUSION

Since a significant percentage of non-small-cell lung carcinoma cases expressed inhibin-alpha, caution should be taken when using inhibin-alpha as the key antibody for exclusion of a lung primary in lung and other organs.