possible reason for your absent pituitary gland
may be accident or any bleed in sellar region which holds the gland. it may be because of other reasons too. but definitely not because of chemotherapy
. I would advice you to go for a complete Heath check up to rule out thyroid, diabetes
and other hormone related problems which may be the cause for depression
. I hope this clarifies your queries and would be glad to answer more if any. regards.