Help please! could cancer cause low blood pressure?

Cancer: Cancer can be associated with low blood pressure. If you have low blood pressure and are otherwise fine, you shouldn't be worrying that you have cancer however. Low blood pressure usually happens late in the course of a serious malignancy.

Not directly : Low BP can occur in cancer due to dehydration or severe infections and some chemotherapy agents. It can also occur if there has been significant weight loss. But isolated low blood pressure in someone who is otherwise healthy is unlikely to be due to cancer.