Spindle cell and pleomorphic
carcinomas are currently grouped among sarcomatoid
carcinomas of the lung. Because of their unusual occurrence, these
tumors have not been properly assessed by immunohistochemistry. We performed a comprehensive immunohistochemical analysis of 86 of these
tumors. Seventy-four pleomorphic
carcinomas (57 with differentiated elements) and 12
spindle cell carcinomas were subjected to immunohistochemistry with
CAM5.2,
cytokeratin (CK) 7,
thyroid transcription factor 1, napsin A, CK5/6, p40,
desmocollin 3, Sox2,
calretinin, and D2-40. The percentage of positive
tumor cells as well as the staining intensity were evaluated and scored. The spindle/giant elements were positive for
CAM5.2 (93%), CK7 (79%),
thyroid transcription factor 1 (41%), napsin A (20%),
calretinin (20%), Sox2 (13%), CK5/6 (9%), p40 (8%), D2-40 (6%), and
desmocollin 3 (3%). Of 29 cases in which immunohistochemistry was performed on spindle/giant cell and corresponding differentiated elements, 21 (72%) showed a consistent staining pattern in both components, whereas in 8 cases (28%), the immunophenotype in the spindle/giant cells was less lineage-specific than in the differentiated component. Therefore, we consider that 42% of
neoplasms otherwise classified as sarcomatoid
carcinoma can be reclassified as
adenocarcinoma and 14% as
squamous cell carcinoma, while the remaining 44% failed to show a more specific immunophenotype. The use of a comprehensive immunohistochemical panel allows reclassification of the majority of sarcomatoid
carcinomas as poorly differentiated variants of
adenocarcinoma or
squamous cell carcinoma. Such reclassification will facilitate clinical management and allow molecular testing and pursuit of targeted treatment strategies. Application of immunohistochemistry should become the standard in the workup of pulmonary sarcomatoid
carcinomas.