My husband's grandfather has prostate cancer that has spread to his bones. Over the past few weeks he has become very weak. We finally got a referral to an Oncolgist which he saw on Monday, who told us that his particular cause was at stage 9 out of 10. Last night he had very low blood pressure reading of 80/60 and this morning 80/40, so he is now at a hospital. What would cause his blood pressure to drop so low?