Ask a health question... Having prostate cancer that is large, will doing kegal exercises cause more damage if it produces a pain?

You cannot hurt. Prostate cancer with kegel exercises, contracting the levator ani muscles, and you use these muscles to control diarrhea, and the urge to urinate. Many times physicians ask you to practice with thse muscles if there is urinary or fecal continence issues. The size of your prostate is irrelevant: you can have symptoms with a large or small gland.
Best do light ones. These exercises are designed to strengthen the pelvic floor. They are usually for women after pregnancy or incontinence or pelvic prolapse, but have benefits for men like for incontinence and stronger erections. Since the prostate is in this area, it might be wise to do light ones for the benefits. Extra pressure would be put there, and it might complicate treatment. Let your doctor know also.