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Tamoxifen: the Breast Cancer preventing drug & increased risk of Ovarian Cysts

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Every week, Dr. Michael White, from the UCONN School of Pharmacy, stops by the Fox CT Morning Extra. This week, he answers a question that came to us from a viewer. She writes: “I am a 43 year old breast cancer survivor and have been taking tamoxifen for 6 years to prevent it from coming back.  I was told initially that five years was enough time but they then said that longer was better.  Today during a routine ultrasound they found an ovarian cyst.  They said it was unlikely to be cancerous but they want me to come back and have another ultrasound in another couple of months.  My questions are, what are ovarian cysts? Can tamoxifen increase the risk of having them? And should I still be on tamoxifen for more than 5 years?”

What are ovarian cysts?

Most ovarian cysts don’t cause symptoms and go away on their own.  If the cysts were found during a physical exam they would then do an ultrasound to see if the mass was fluid filled or solid.  It looks like your was found on ultrasound and your doctor is less worried about it being cancerous based on what she saw.  I few people with these noncancerous fluid filled cysts can be harmed if they rupture or bleed but that is rare.  Usually in these cases they will do repeat ultrasounds in 1-3 months to see if they are growing or going away, exactly what your doctor is recommending.  However, if you get severe abdominal or lower back pain, including pain with intercourse, contact your doctor right away because that may mean your cyst is more dangerous.

Can Tamoxifen cause ovarian cysts?

Yes, if you are a younger women who is still menstruating, definitely.  In three different observational studies tamoxifen use was found to increase the risk of developing these cysts and almost 40-60% of younger premenopausal women had at least one over the course of therapy but older postmenopausal women on tamoxifen did not have an increased risk.

If Tamoxifen can cause ovarian cysts, are there benefits to taking them for more than five years?

Here the recommendation is very strong, yes there are additional benefits for 10 years versus 5 years of tamoxifen therapy.  Two large randomized trials, the best type of evidence available, shows an improvement in survival rates and reductions in having a breast cancer relapse if you use 10 versus five years of therapy.  Now if you as an individual are developing ovarian cysts that get to be too large or are prone to rupture and bleed, it may not be worth it for you.  Tamoxifen can also rarely cause other side effects like endometrial or uterine cancer, which is why they were doing the ultrasound in the first place, and blood clots and for those people the benefit isn’t worth the risks.  It sounds like the benefits for you, at the present time, outweighs the risks but continue to listen to your doctor, it seems like he or she has been right on so far.