Do malignant neoplasms put out chemicals that do strange things to your body?

Yes. Malignant neoplasms (otherwise known as cancers) produce a variety of different chemicals. Some of these chemicals are present in your body, but are produced in might higher levels than normal. Some tumors produce insulin, others produce calcium regulating hormones, just to name a few. The fancy name for some of these are paraneoplastic syndromes.