That certainly is true and can happen....but is extremely rare and unusual...any little remnant left behind could undergo malignant degeneration. It is tragic when that happens because the odds of diagnosing this in a timely manner is even less than the low liklihood of finding a primary ovarian malignancy in a "normal" ovary.
Since you are being so nice about answering questions, I have a strange one for you.
I had my hysterectomy 9 years ago. My surgeon said he left one ovary to avoid the menopause problems. The GYN said I should still have paps even tho the cervix was gone, but I only went one year, didn't make sense to me.
Now....2 years ago, I went to a gyn about some hormone questions. He does an ultrasound in his office and low and behold I have 2 ovaries. He said that they can regenerate. I guess I have to believe either that or my surgeon lied to me. Any guesses??? I'm feeling like a lizard or an alien or something regenerating parts....