Microtubule-associated proteins (MAPs) are a major component of cytoskeleton family
proteins associated with microtubule assembly. MAP-2 has been shown to be specifically expressed in neuronally differentiated cells. Pulmonary
neuroendocrine carcinomas such as
carcinoid tumors and
small cell carcinomas are derived from neuroendocrine cells. We hypothesize that neuroendocrine cells may also express MAP-2, and therefore, MAP-2 may be used as a marker for pulmonary
carcinomas of neuroendocrine differentiation. To investigate the utility of using MAP-2 expression to separate pulmonary neuroendocrine from non-
neuroendocrine tumors, we examined the expression of MAP-2 immunohistochemically in 100 cases of pulmonary
carcinomas. The immunoperoxidase method with
antigen retrieval was used to characterize the expression of MAP-2,
chromogranin,
synaptophysin, and
neuron-specific enolase in 25
small cell carcinomas, 25
carcinoid tumors, 25
adenocarcinomas, and 25
squamous cell carcinomas. All
tumors were lung primaries. All 25 cases of
carcinoid tumors (100%) as well as 23 of 25 cases (92%) of
small cell carcinomas were positive for MAP-2. Four of 25 cases (16%) of
adenocarcinomas were positive for MAP-2 and
synaptophysin. Among the 25
squamous carcinomas, 4 cases (16%) were positive for MAP-2, 2 cases (8%) were positive for
synaptophysin, 11 cases (44%) were positive for
neuron-specific enolase, and none was positive for
chromogranin. In conclusion, MAP-2 is a new sensitive and specific marker for the pulmonary
tumors of neuroendocrine differentiation. We recommend that MAP-2 be added to immunohistochemical panels to separate non-neuroendocrine from neuroendocrine lung
tumors.