Cancer is a huge problem, since it is actually a collection of a lot of different diseases in different places, resulting from mutation of the genes and invasiveness as the common characteristic. All cancers are different.
Carcinoid tumor is a good illustration. These are so called neutoendocrine tumors. They are slow growing, and are usually not detected until they are quite advanced. They can be located in different organs such as the gastrointestinal tract and the lung.
In their vicinity they produce symptoms characteristic of the area; trouble swallowing, nausea, vomiting, constipation and abdominal pain for gastrointestinal carcinoid, and cough, wheezing, shortness of breath and chest pain for those located in the lung.
Many advanced cancers can produce weight loss, muscle pain and fatigue In addition to symptoms characteristic of their location. The special characteristic of carcinoid tumors is that they may secrete substances that produce diverse symptoms such as flushing of the skin, sudden diarrhea and vomiting and, strangest of all, heart valve leakages.
Diagnosis of carcinoid tumors is often made by checking for serotonin or chromogranin-A in the blood, and 5-Hydroxy indolacetic acid ( 5-HIAA) in the urine, and locating the tumor with Imaging such as CT and MRI.
It is usually treated best for surgery, but cell surface somatostatin can be targeted for hormone therapy, and targeted radiotherapy with PRRT. It is very much to the advantage of the patient if she has a tumor with specific hormone or other marker that can be targeted for treatment, such as a breast cancer with estrogen receptors that can be targeted by tamoxifen.
Please check the accompanying mayo clinic article for more information.