Do I Have Ovarian Cancer?

Risk of Malignancy Index Helps Determine Risk That a Mass is Ovarian Cancer

If your doctor finds an ovarian mass after viewing an ultrasound, or feels one on exam, what are the chances that what's been discovered is ovarian cancer? That is a difficult question to answer with certainty, and the only way to know for sure is surgery. However, surgery is not without risk and may not actually be needed to come to a confident idea of what the mass actually likely is. For example, a mass may be characteristic of a cyst, which has a good chance of going away on its own if you are not post-menopausal.

(If you are post-menopausal, the risk is higher, but still is often not cancer.)

Fortunately there is something called the Risk of Malignancy Index (RMI) which can help sort things out. There are several versions of the RMI, and all of them predict the risk of malignancy (risk that the mass is cancerous) with similar accuracy. This version has been tested several times by different researchers over the years.

There are three main factors used when determining the RMI in your case: age, level of CA-125 (a tumor marker) and the score of your ultrasound. Your radiologist will determine your ultrasound score, basing it on how complex the ovarian cyst or mass looks. Are there solid areas? Are there dividing membranes within the mass, known as septations? One point is assigned for each of the following: a multi-locular cyst (sort of like a cluster of large grapes),solid areas, evidence of spread (metastases), abnormal free fluid (ascites), or masses on both ovaries.

If you're interested in getting technical, the basic formula is:

  • RMI= U x M x serum CA-125 level
U represents the ultrasound score, from 0 to 5. M is a menopause score where 1 is assigned to those who are pre-menopausal, and 3 is assigned to those who are post-menopausal. The last factor is the numeric value of your CA-125 level; a value of 35 or lower is considered normal.
You simply multiply the U, M and CA-125 values to get RMI.

You Have Your RMI Score. What Does it Mean?

An RMI score greater than 200, calculated in this fashion, is considered suspicious. If it exceeds 250, the chance that what you have is cancer is very high. However, the key word is “chance.” Remember that this index helps sort things out, but does not prove one way or the other whether or not you have cancer for sure. For example, if you are under 50 and have endometriosis, or have other reasons for CA-125 to be elevated, the RMI may be falsely high. Therefore, you may not have cancer. On the other hand, some cancers do not produce CA-125, so the RMI may be falsely low.

The RMI may help you and your doctor determine the next step if an ovarian mass was found. One reason to consider calculating the RMI is that it can help decide whether or not a gynecologic oncologist should be available for your surgery, if that is required. The higher the RMI, the more it may be prudent for one to be present.
Keep in mind that this is only one piece of the puzzle in deciding what to do, and it does not apply to all types of ovarian cancer. A thorough discussion with your doctor about your specific situation is required. If there is any lingering doubt, consider a second opinion with a gynecologic oncologist.

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Jacobs I, Oram D, Fairbanks J, Turner J, Frost C, Grudzinskas JG. "A risk of malignancy index incorporating CA 125, ultrasound and menopausal status for the accurate preoperative diagnosis of ovarian cancer." Br J Obstet Gynaecol. Oct 1990.


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