Lung Cancer.pdf

76 P. Tamboli and J.Y. Ro
Other Malignant Epithelial Lung Tumors
In addition to the above-mentioned malignant epithelial tumors, carcinomas
of the salivary-gland type may arise from the bronchial glands. These
include mucoepidermoid carcinoma, adenoid cystic carcinoma, acinic cell
carcinoma, epimyoepithelial carcinoma, and malignant mixed tumor. All
these tumors have morphologic features similar to their namesakes that
originate in the salivary glands. Finally, malignant epithelial tumors may
occur that cannot be classified in any of the above-mentioned categories;
these tumors are termed “unclassified carcinoma.”
Ancillary Evaluation Techniques
Immunohistochemical Staining
Immunohistochemical stains are used regularly in our laboratory for the
routine diagnosis of lung tumors and also for research purposes. These
stains are routinely used to differentiate primary pulmonary adenocarcinoma
from adenocarcinoma that has metastasized to the lung, to determine
the neuroendocrine status of tumors, and to distinguish lung adenocarcinoma
from epithelioid mesothelioma.
Distinguishing Primary Tumors from Metastases
Morphologically, primary adenocarcinoma of the lung may be remarkably
similar to metastatic adenocarcinoma. The presence of multiple nodules in
the lung in a patient with a history of a primary adenocarcinoma at another
site often leads to the presumptive diagnosis of metastases. However,
multifocal adenocarcinoma of the lung is not rare and needs to be
distinguished from metastases. Also, some patients may develop a second
primary tumor in the lung. Hence, during the evaluation of a solitary nodule
of adenocarcinoma in a patient with a known history of an extrapulmonary
tumor, primary adenocarcinoma of the lung needs to be ruled out.
Pulmonary adenocarcinomas stain positive for thyroid transcription
factor 1 (TTF-1), cytokeratin 7, and surfactant apoprotein A but do not
stain for cytokeratin 20. TTF-1 is a relatively new marker that is very useful
for distinguishing between adenocarcinomas of pulmonary origin and
adenocarcinomas from other sites (Ordonez, 2000a,b). TTF-1 is a transcription
factor expressed by type II pneumocytes and Clara cells in the
lung and also expressed in the thyroid gland, parathyroid gland, anterior
pituitary, and tumors of thyroid gland and lung origin. Most carcinomas
of the lung express TTF-1; however, the percentage of cases showing expression
varies according to the subtype. Most adenocarcinomas of the
lung and most small cell carcinomas express TTF-1; a smaller percentage
of squamous cell carcinomas and large cell carcinomas express TTF-1.
TTF-1 is useful for differentiating primary adenocarcinoma of the lung