[Contribution of immunohistochemistry to the management of lung cancer: from morphology to diagnosis and treatment].

Immunohistochemistry (IHC) has become an indispensable tool in pathology. For proper interpretation, results must be read with knowledge of the diagnostic, clinical, and morphological circumstances. We detail here the contribution of IHC to the classification of lung cancer: small-cell lung cancer and other neuroendocrine tumors, basaloid carcinoma, large-cell carcinoma. Using IHC techniques, pathologists can now determine with certainty that an intrathoracic adenocarcinoma is primary or secondary. The distinction is less clear for large-cell carcinoma or squamous-cell carcinoma, or for tumors with a pleural or mediastinal presentation. IHC is also useful as a diagnostic aid for rare entities: carcinomas with an unusual morphology (alpha-fetoproetin secretors or beta-HCG secretors), melanomas, lymphomas, sarcomas. By demonstrating the presence of carcinomatous cells within the neighboring structures (pleura) or lymph nodes, IHC contributes to lung cancer staging, particularly when there are few of these elements morphologically difficult to distinguish. Finally, IHC contributes to prognosis (proliferation markers, differentiation markers) or prediction of therapeutic response (chemotherapy or targeted therapies). IHC studies may also be requested in a forensic setting, for example to demonstrate that the lung cancer observed in a patient exposed to asbestosis is primary. In light of these different situations, a wide panel of antibodies is required. Other morphological techniques such as hybridization in situ or molecular biology techniques will further complete the histological diagnosis in the future.