Interestingly, neuroendocrine cells are present in higher numbers in the lungs of smokers
Similar origin to carcinoids found in GI tract, gallbladder, and pancreas
Bronchial carcinoids have similar neuroendocrine properties to APUDomas, pheochromocytomas, medularry carcinomas of thyroid, etc.
Metastasis: usually local and well-defined, but they may metastasize via lymphatic (to hilar/mediastinal nodes) or hematogenous spread (to liver/bones/brain/adrenals)
Size and degree of differentitation may be related to risk of metastasis
Local nodal mets occur in 10% of cases, while distant mets occur in 3% of cases
Serotonin-Producing Carcinoids: these are unusual in the lungs (and only 50% of those with elevated serotonin metabolites have the carcinoid syndrome)
Pathology
Small uniform cells with acidophilic cytoplasm and finely stippled chromatin
EM: neurosecretory granules
Immunohistochemical stains: positive for neuron-specific enolase, chromogranin-A, synaptophysin, serotonin, and other neurosecretory cell markers
Neuroendocrine Carcinomas (also known as Atypical Bronchial Carcinoids): variant with larger cell size and at least some neurosecretory neoplastic features
These have higher incidence of local nodal and distant mets than normal carcinoids
Diagnosis
LFT’s: may be useful in staging
Serum Serotonin/Urinary 5-HIAA: elevated in <25% of cases at time of diagnosis
Note: only 50% of patients with elevated urinary serotonin metabolites have the carcinoid syndrome
Thoracotomy with Resection: curative treatment of choice
Hilar mediastinal node sampling: indicated for tumor >2 cm or poor differentiation
Persistent elevation of 5-HIAA post-op merits metastatic work-up
Tracheal Carcinoid: amenable to tracheal sleeve-resection
FOB: laser/fulguration have high recurrence rate
Procedure of choice for poor surgical candidates
XRT (45-50 Gy): palliative (80% have partial/complete response but cure is not expected)
Spinal and bone mets may be treated well with XRT
Liver and lung mets are not well-treated with XRT
Chemo (5-FU/Streptozotocin/Cytoxan/Doxorubicin): <40% response rates, with no survival benefit
Hepatic arterial therapy: useful for isolated liver mets
Octreotide: useful for symptoms of Carcinoid syndrome in metastatic disease (does not decrease tumor burden or prevent long-term effects of serotonin on heart)
Tachyphylaxis: may occur
Interferon-alpha: may induce tumor regression (SE limit use, but responders may be identified in advance)
Prognosis
Median Survival: >10 years (some cases survive <1 year)
10 year survival: >95%
In patients with small, typical carcinoid, completely resected
10 year survival: <55%
In patients with systemic symptoms, unresectable tumors (including positive hilar nodes)
Male Patients: poorer outcome
Atypical Bronchial Carcinoid (Neuroendocrine Carcinoma): <50% long-term survival (even with small tumor)