Is it safe to take pentostatin while pregnant or breastfeeding?

No. Pentostatin is a cancer drug. It works to stop cancers by killing cells that are dividing. It can cause damage to a developing baby. If you are on pentostatin and become pregnant, immediately tell your doctor. If you are wanting to become pregnant and are on pentostatin, talk to your doctor about how long after the treatments are over before you can try for pregnancy.
Avoid if possible. Pentastatin has a profound immunosuppression effect. Only your doctor can outline the risks vs benefits for you.