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The Dark Side of Aromatase Inhibitors – Part 1

I divided this topic into a couple posts because I’m working on being less wordy and more concise in my writing. Part one will be my attempt to convey general information about aromatase inhibitors. Part 2 will be focused on my personal experience – rant, so stay tuned.

Update:  You might want to read and download, Endocrine Therapy – Managing & Making Decisions About Your Aromatase Inhibitor Medication.

Many breast cancer tumors are estrogen positive (ER-positive), progesterone positive (PR-positive), or both (ER-positive and PR-positive). Mine was both.

By the way, this information about your tumor(s) is provided in your pathology report. You should have a copy of this report so you can familiarize yourself with your unique cancer’s biology, even though this might sound like the last thing you want to do after your diagnosis.

Be sure to ask for a copy if you don’t/didn’t receive one.

If a woman is ER and/or PR positive, her oncologist might very likely prescribe an aromatase inhibitor after surgery, chemotherapy or radiation as part of her adjuvant therapy treatment plan. The intent is, of course, to prevent recurrence.

There are three kinds of aromatase inhibitors (referred to as ‘AIs’ from here on out) that have been FDA approved:  anastrozole (Arimidex®), letrozole (Femera®) and exemestane (Aromasin®).

Basically, these drugs block tumor growth by lowering the body’s natural supply of estrogen.

How do they do this?

These drugs don’t allow the food supply (estrogen) to get to the tumor because they block the aromatase enzyme, which is needed for the production of estrogen.

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Hence the name, aromatase inhibitors.

AIs are often prescribed for post-menopausal women because they don’t block estrogen produced by the ovaries, but do inhibit estrogen production in other body tissues. If you’re not post-menopausal, the benefit’s not there. For pre-menopausal women with estrogen positive cancers, Tamoxifen is still the recommended hormonal adjuvant therapy drug most often prescribed.

Before cancer, I didn’t even know that in addition to the ovaries other body tissues also produce estrogen, but they do.

As I understand it, there isn’t a lot of difference between the three AI drugs. One difference however, is that Aromasin® is an irreversible aromatase inhibitor (stops aromatase enzyme’s production process permanently) while the other two are not.

Studies seem to indicate the effectiveness of the drugs in preventing recurrence is pretty much the same.

AIs have become standard treatment for adjuvant hormonal therapy for many post-menopausal breast cancer patients. You gotta shut that estrogen production line down, and that’s what AIs do.

I remember the day when oncologist number one showed Dear Hubby and me all those mind-boggling, ten-year survival odds charts. The charts indicated if I agreed to add Arimidex® as part of my adjuvant treatment plan, I would gain another six percentage points for my staying-alive plan.

I was on board. I wanted those additional six percentage points on my side.

Who wouldn’t?

And now on to the dark side of AIs — in case you can’t guess — but I’m betting you probably can, this would be the nasty side effects.

Every person is different. Just because you’ve heard horror stories about unpleasant side effects, don’t assume you’ll experience the same.

Having said this, some of the side effects are fairly common and even somewhat predictable.

Generally speaking and maybe even mildly comforting to know (then again, maybe not), the side effects of all three AIs are similar.

The most-often mentioned side effects are:  joint pain, bone loss, bone fractures, lowered libido, hair loss/thinning, weight gain, hot flashes and sleep issues to name a few. (Yikes, do we really need more?)

The side effects are often not addressed adequately, if at all, by oncologists. This is too bad because side effects can, at the lesser end of the spectrum, be highly annoying and at the worst end, be extremely debilitating.

I speak from experience on this as I have had some very unsettling side effects myself.

In fact, side effects (mine anyway) are the focus of The Dark Side of Aromatase Inhibitors – Part 2.

Get your rants ready too!

Note:  Please remember that while I always strive for accuracy in facts I share, my posts also generally include my thoughts and opinions and are not intended to be medical advice specific to you. Please discuss all concerns with your doctor.

Are you on an aromatase inhibitor or do you know someone who is?

Are you on Tamoxifen?

If so, how are things going and are the side effect issues (if you have any) being adequately addressed?

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Update:  You might want to read and download, Endocrine Therapy – Managing & Making Decisions About Your Aromatase Inhibitor Medication.

The dark side of aromatase inhibitors, part 1 #breastcancer #endocrinetherapy

The Dark Side of Aromatase Inhibitors


Lynn Wilson

Monday 16th of May 2022

In 2013 I was diagnosed with stage 1 breast cancer. After a lumpectomy and radiation my oncologist first put me on Arimidex. The side effects were horrible and I also had a heart surgery coming next. I had complete insomnia and severe joint pain. He next put me on Aromasin which caused all of my top teeth to crack off requiring me to get dentures which has taken away any pleasure of eating. I also broke 6 toes and 2 ribs. After that I said no more. I am still cancer free.


Wednesday 18th of May 2022

Lynn, I'm so sorry you've had to deal with all that and don't blame you for saying, no more. Glad you're doing well. Thank you for sharing.


Wednesday 11th of May 2022

I stopped my aromatase inhibitors It should be mentioned that this is chemo in pill form In addition to a broken femur the sexual side effects are horrible In addition to no sex drive at all, I now have a foul vaginal odor So great not only do I feel dead inside but I smell The smell makes me feel vile and disgusting


Friday 10th of April 2020

Dear Friends, I’ve been on Letrozole for 16 days. I was diagnosed and treated for breast cancer in 2002, age 44. I had a double mastectomy, chemo, radiation and then my period returned so I elected to have a double oophorectomy. I was disease Free for 17 years. For weeks ago a lung biopsy revealed primary breast cancer. It’s a 2x3 cm tumor. I took Arimidex 17 years ago and almost couldn’t walk after a few weeks. So, I stayed away from AIs. I was hopeful that I may be able to tolerate AIs this time to starve my lung tumor. After 16 days of it in my system, I developed pain in my sternum that radiated across my chest. I woke up in the middle of the night with the most severe upper back pain of my entire life. My oncologist told me to hold my Letrozole for a week. I’m still nauseated and in pain but I have hope that I’ll recover. I read it takes about 2 to 6 weeks for estrogen production to be halted with the AIs. I was wondering if I actually was experiencing angina from the complete depletion of my estrogen. After all, the heart is a muscle and maybe I need hormones to keep it healthy. I’m not a melodramatic person or a hypochondriac. My acute pain was real and very frightening. I’m an ICU nurse of 36 years. Thank you, everyone, for sharing your experiences. As my dearest oncologist Dr. Brennan said to me in 2002,”You’re a statistic of one and you matter.”


Wednesday 26th of February 2020

Hi Ladies - I thought I'd put in my two cents here. As you've all noted, everyone is different when it comes to side effects. I started on 20mg Tamoxifen in 2015, and stayed on for two years despite severe leg and foot cramps. My oncologist said he never heard of this, (and he must be in his 70s.) I can't understand how he wasn't aware of this side effect, when all I had to do is google it and saw tons of women who suffered the same thing. After two years I switched to Letrozole and had almost every side effect out there. Which is weird because I've never been very sensitive to drugs / pain killers. Anyway, before long I felt like I was 90 (I was in my mid-50s), my hands were stiff and joints were sore - could hardly open and close them in the mornings, I had a mild depression and horrible nightmares (which I read some other women had) No hair loss or weight gain though. Had problems with my feet/ heels. After a while switched to Exemestane. It wasn't quite as bad but did have a lot of problems with my feet, and I'm a walker, so that really disrupted my lifestyle. It felt like plantar fasciitis and other heel pain. Hands were still stiff with swollen joints. And cholesterol shot way up which is apparently another side effect. So after a year and a half on AIs I'm back on Tamoxifen for my final year. (done in June!) But just 10mg (1/2 dose) because of the leg and foot cramps. I try to do more with diet, exercise, getting natural aromatase inhibitors in my food (incl flaxseed) and intermittant fasting (some positive evidence there) So, yeah, AIs suck. Hang in there, everyone!


Wednesday 19th of February 2020

February 19, 2020 I have taken Tamoxifen for 547 days. Currently, I am on a break for 30 days and am checking out if I can take this med every other day since there seems to be a lot left in your body being a steroid for a period of time. My only downside of taking this drug is hair thinning. I used to have really thick hair. So some of this may be my age of 72. I am now taking laser therapy with a bonnet. Before starting Tamoxifen my doctor wanted me on A!'s. I read all the whore stories and looked at all the lab trails. I drew a line where the Tamoxifen is less effective after 2 years while the A!'s supposedly have better longer life expectancy. I decided when I reach 2 yrs on this drug, I will look to see what else in on the market and their results and make a decision at that time. My surgeon, the best in Charlotte, was glad I chose Tamoxifen because the A!'s could cause bone fractures at my age. Luckily my cancer was small and I decided not to have chemo but went for the month of radiation. Two good check ups so far so ladies just keep reading those trials and see what might be new on the market. Pulling estrogen out of your body is not healthy. It's there for a reason!!!

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