Lung Cancer.pdf

Pathologic Evaluation of Lung Cancer 59
Figure 4–1. Algorithm for pathologic diagnosis of lung nodules.
processes may result in pulmonary nodules that mimic neoplasia, the first
step in the algorithm is to decide whether the nodule is neoplastic or nonneoplastic.
If the lesion is neoplastic, the next step is to decide whether it is benign
or malignant. Benign tumors are usually expansile or encapsulated, are
well-differentiated, resemble the tissue of origin, have a slow rate of
growth, have no mitoses or rare normal mitoses, and—most important—
do not metastasize. Malignant tumors show an infiltrative growth pattern,
are usually not encapsulated, have an atypical structure with anaplasia,
grow rapidly, have high mitotic counts and abnormal mitoses, and have
the ability to metastasize.
Because metastases in the lung are more common than primary lung
tumors, the next step once a malignant lung tumor has been identified is
to decide whether it is a primary lung tumor or a metastasis. Primary
lung tumors are usually single; usually have an ill-defined margin, with
dysplasia in the adjacent epithelium; and occasionally show vascularlymphatic
invasion. Metastases, in contrast, may be single or multiple, usually
are small, possess a well-defined margin, are not associated with dysplasia
in the adjacent epithelium, and frequently show vascular-lymphatic
invasion.
Primary malignant tumors of the lung may be epithelial or mesenchymal.
Epithelial tumors are generally arranged in nests or cords and have
oval, round, or polygonal cells set within a desmoplastic stroma with blood