The following is true about bronchial carcinoids-

Ref:Textbook of pathology (Harsh mohan) 6th edition,page no.503 BRONCHIAL CARCINOID AND OTHER NEUROENDOCRINE TUMOURS Neuroendocrine tumours of the lung represent a continuum spectrum of lung tumours with progressively increasing aggressiveness which include: typical carcinoid (least aggressive), atypical carcinoid, and large cell endocrine carcinoma, and also small cell carcinoma (most aggressive). All these tumours arise from neuroendocrine (Kulchitsky) cells of bronchial mucosa. Formerly, bronchial carcinoids used to be classified as 'bronchial adenomas' but now it is known that they are locally invasive and have the capacity to metastasise. Bronchial carcinoids tend to occur at a younger age than bronchogenic carcinoma, often appearing below the age of 40 years, and are not related to cigarette smoking. CLINICAL FEATURES. Bronchial carcinoids occur at a relatively early age and have equal sex incidence. Most of the symptoms in bronchial carcinoids occur as a result of bronchial obstruction such as cough, haemoptysis, atelectasis and secondary infection. About 5-10% of bronchial carcinoids metastasise to the liver and these cases are capable of producing carcinoid syndrome.