Let me try this again one ovary larger than other ovary only shows simple folllicular cyst on ultrasound nothing abnormal can cancer present a just an enlargrment with nothing abormal on ultrasound?

Not likely. Ovaries are very active organs with monthly changes, enlarging and shrinking. Cysts come and go. Usually pelvic ultrasound is repeated after 4-6 weeks. A tumor may persist. Cancer may continue to grow. In medically literature, a size greater than 5 cm may prompt surgical intervention. Again, there are no way to rule out cancer until the ovary is removed.
It can. Although generally cancers show up as complex cysts, often containing irregular material in the cysts on ultrasound. Biopsy is the best way to determine if it is cancer.