Dropping platelet counts. Appreciated.

My father in law was to have carpal tunnel surgery last Friday. He arrived at the hospital and was taken to pre-op, where he was prepped for surgery. IV fluids were started and all medical interviews completed; Anesthesiologist included. Ten minutes before he was set to enter the OR for surgery, the Doctor came in and informed my father in law that he would not be able to proceed with the operation due to low platelets. My Father in law was told he has to see a Hematologist Oncologist ASAP. His counts had dropped from 111 to 95 in a only a week. He is very very fatigued and not acting like his normal self (outgoing and always joking). This is NOT normal for him and it has me VERY concerned. My husband and his father are very close and not having an answer of any kind is tearing him up. It breaks my heart. I am looking for answers that are frank and straightforward as to what we could be facing. Any wisdom that can be provided is greatly appreciated. Thank you and God Bless!