71. A 50-year-old man presents with increasing chest pain, bloody sputum, and weight loss over the past 3 months. A high resolution CT scan reveals a mass circumscribing the right main bronchus, extending into its lumen. Histologic examination of an open-lung biopsy is shown in the image. Electron microscopy shows numerous neuroendocrine granules withintumor cells. What is the appropriate diagnosis?
Squamous cell carcinoma
Answer : C Carcinoid tumor
Carcinoid tumors account for 2% of all primary lung cancers.
They comprise a group of neuroendocrine neoplasms derived from the pluripotential basal layer of the respiratory epithelium.
Carcinoid tumors occur most often in the wall of the major bronchus and may protrude into its lumen.
The tumors are characterized by an organoid growth pattern and uniform cytologic features.
Carcinoid tumors exhibit a neuroendocrine differentiation similar to that of resident Kulchitsky cells. The indolent nature of carcinoid tumors is reflected in the finding that half of the patients are asymptomatic at the time of presentation, but regional lymph node metastases occur in 20% of patients.
Atypical carcinoids exhibit a more aggressive behavior. Neuroendocrine features are absent in the other tumors.