Figure 3

Spectrum of pulmonary neuroendocrine cell (PNC) proliferation and its intimate association with PSH. (A) Typical carcinoid tumor, 5.5 mm in size, composed of uniform short-spindled or oval shaped cells. (B) Carcinoid tumorlet admixed with PSH in a single nodule, with PSH on the left (dotted arrow), tumorlet on the right (arrow). (C) Foci of PNC proliferation highlighted by synaptophysin staining beneath airway epithelium (arrows). (D) Positive chromogranin staining in a tumorlet, in contrast to surrounding negative PSH areas (H&E stain and polymer method, original magnification, (A) and (D) × 20, (B) and (C) × 40).