Is a carcinoid tumor deadly?
It can be, yes.
A carcinoid tumour is a type of cancer that starts in neuroendocrine cells (neuro- meaning nerves and endocrine meaning cells that produce hormones, so these are tumours that start in the nerve cells of endocrine producing organs in the body).
Carcinoid tumours are slow growing and often don't produce symptoms.
Depending on where the tumour develops and the type of tumour it is greatly affects the 5-year survival rate.
This link has a lot of useful information about carcinoid tumors: http://www.cancer.net/cancer-types/carcinoid-tumor/overview