Does nipple discharge always indicate cancer among men?

No: Nipple discharge may be due to many different factors other than cancer, in a man or a woman. Discharge that is watery or bloody, spontaneous, and/or coming from one nipple is concerning for a cancer. If a man has this type of discharge and no palpable lump in the breast, the next test to get is a mammogram.

Not always: Certainly suspicious, especially if the discharge is clear. You should see a doctor, and, obtain a good physical exam, mammogram and ultrasound to evaluate.