The CA 125 test is not accurate at diagnosing ovarian cancer. Even absent cancer, you can get a very high result. A friend and I had the same type of benign / non-cancerous ovarian cyst. My CA 125 was in the 30's (normal range) while hers was over 1000. Neither of us had cancer.
Since your cyst is fluid-filled it's more than likely benign. I've never heard of an SIS procedure. From what you said it sounds like he did a biopsy... I assume from the fluid in the cyst? Is your cyst 10 x 13 mm or cm? If it's mm then it will likely resolve on its own.
If you do end up needing surgery, you shouldn't need any organs removed, not even your ovary (oophorectomy) and certainly not your uterus (hysterectomy). A surgeon with good cystectomy skills should be able to remove just the cyst so you can keep your ovary (as well as uterus and other ovary) and its health promoting hormones.
The uterus, ovaries and tubes work together and have lifelong functions - anatomical, skeletal, hormonal / endocrine, and sexual. Removal of even one ovary has been shown to increase risk for some health problems. Ditto for removal of the uterus. And removal of both ovaries has a long list of increased health risks including heart disease, the #1 killer of women. To put it in perspective, only about 1 in 100 women dies of ovarian cancer (1 in 73 is diagnosed with it) while 1 in 3 women dies of heart disease.
My friend and I were over-treated as many women are for gynecologic problems. Our gynecologists removed all our organs and neither of us were properly informed of our treatment options and the debilitating and never-ending problems caused by the removal of our organs (castration).
Please do your research and make sure you have all the information you need to understand your treatment options and the consequences associated with them.
Let us know what more you find out.