There should be a really easy answer to this question. Unfortunately, there's not, and that's partly because we're still in fairly early stages of the research.
As you may be aware, the average age of diagnosis for ovarian cancer is 61. We actually do these opportunistic salpingectomies on people who on average are in their early forties. We haven't had all the follow-up time that we need to really answer that question.
Our 2022 article in JAMA Network Open was the first prospective study of opportunistic salpingectomy done for the purpose of ovarian cancer prevention. It is important, because it means the surgeon is removing the entire fimbriated end of that Fallopian tube to really reduce the risk.
In that study, we saw zero high-grade serous cancers in the approximately 26,000 people who had an opportunistic salpingectomy. This was statistically significantly lower than the number that we would have expected to see if the cancers had been arising at the same rate as they were in the control groups, which were people who had hysterectomy or tubal ligation alone.
We haven't had enough follow-up time to give the specific number needed to treat, but we have a lot of preliminary evidence that suggests that opportunistic salpingectomy is going to be very effective at reducing the risk of high-grade serous ovarian cancers.