Lung Cancer.pdf

70 P. Tamboli and J.Y. Ro
noma. Cigarette smoking is an important risk factor for all neuroendocrine
tumors. However, while almost all small cell carcinomas and large
cell neuroendocrine carcinomas affect smokers, 20% to 40% of carcinoid
tumors occur in nonsmokers. Both types of carcinoid tumor may be found
in patients with type I multiple endocrine neoplasia syndrome, but there
is no association between this syndrome and the other 2 neuroendocrine
tumor types (small cell carcinoma and large cell neuroendocrine carcinoma).
Typical Carcinoid. Typical carcinoid of the lung is morphologically similar
to carcinoid tumors seen in other sites. Tumor cells are arranged in
nests, trabeculae, or cords or form rosettes. The tumor cells are uniform,
small, have a small amount of eosinophilic cytoplasm, and have round or
oval nuclei with finely granular chromatin and rare small nucleoli. These
tumors may show increased cellularity, nuclear atypia, and rare mitoses.
By definition, typical carcinoids measure 5.0 mm or more, have fewer than
2 mitoses per 10 high-power fields, and lack necrosis. Up to 15% of typical
carcinoids metastasize to the regional lymph nodes, but these tumors
rarely metastasize to distant sites or cause death.
Atypical Carcinoid. Atypical carcinoids have morphologic features similar
to those of typical carcinoids except that atypical carcinoids are characterized
by necrosis or 2 to 10 mitoses per 10 high-power fields (Figure 4– 4),
are more cellular, and have a greater degree of nuclear atypia. Neuroendocrine
tumors with similar morphologic features but with more than 10
mitoses per 10 high-power fields are classified as large cell neuroendocrine
Figure 4–4. Atypical carcinoid. The tumor is arranged in nests and shows mitoses
and necrosis.