Peripheral carcinoid tumour arises in the peripheral lung, often immediately beneath the pleura.
It is usually asymptomatic and diagnosed incidently as a nonencapsulated gray to tan nodule not related to a bronchus.
Microscopically, it is composed of spindle cells, resembling smooth muscle cells, and is arranged disorderly with a certain degree of pleomorphism.
Spindle shaped cells in Peripheral Carcinoid
The stroma can be prominent.
When multiple tumors are present, may produce restrictive and obstructive lung diseases.
Like central carcinoid it may acquire paraganglioma-like features, due to the presence of S-100 protein-positive sustentacular cells.
Amyloid and melanin may be found, and calcitonin reactivity may be demonstrated immunohistochemically.
These features establish a close histogenetic link between peripheral lung carcinoid , thymic carcinoid , and thyroid medullary carcinoma.
Most other immunohistochemical reactions are similar to those of central carcinoid tumour.
Prevalent TTF-1 positivity in carcinoid tumorlet and peripheral carcinoids suggest that they may be histogenetically distinct from the central carcinoids, which are typically composed of TTF-1-negative, more rounded cells.
A case has been reported in association with Merkel cell tumor of the skin.
The prognosis of peripheral carcinoid tumor is excellent, regional lymph node metastases are very rare, and most cases are cured by limited surgery.
Lobectomy is preferable to wedge resection because of possibility of multicentricity. Enucleation should not be attempted.
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