My 91 yo father has pleiomorphic dermoid sarcoma that started on the top of his head and went into his skull and lungs. He received radiation for his head and has had 6 does of keytruda which improved everything including his breathing. Suddenly he developed severe muscle weakness and anemia in which he could not get out of bed. He was placed in the hospital and received iron injections and is in an extended care facility for physical therapy . The site on Keytruda states severe expression for some of his side effects. I am an RN and have not used that terminology before. Is the above to be expected due to the drug or is this just a symptom of his declining and what does expression mean?