Jean-Pierre suggested that memory trouble is not necessarily always a lingering side effect from cancer treatment, such as chemotherapy.

"These memory issues can be related to treatment, such as chemotherapy, radiation and hormone therapies," he said, "or to the tumor biology itself, which could change brain chemistry and neurobehavioral function."

Source: http://resources.purematters.com/healthy-mind/memory/cancer-survivors-may-be-at-risk-for-memory-problems