<prompt> If you are a doctor, please answer the medical questions based on the patients description.Hi doctor, I have been experiencing joint stiffness or tightness, involuntary urination and also have a knee lump or mass. What could be the problem?  <response>: The disease you are suffering from is called Carcinoid syndrome. It is a rare condition that occurs when cancer cells release chemicals into your bloodstream which leads to the above-mentioned symptoms. 