Tamoxifen vs Aromatase Inhibitors as Adjuvant Therapy

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Tamoxifen (what is Tamoxifen?) has been the most popular choice as – to put it technical words we’ll explain – “adjuvant therapy for post-initial treatment, early-stage breast cancer that is estrogen receptor positive.”  Basically, it helps prevent breast cancer from coming back.

You may have heard, however, that recent research may indicate that in post-menopausal women, a class of drugs called aromatase inhibitors (AI) may be more effective for preventing breast cancer from coming back.

There are indeed some positive benefits that aromatase inhibitors may have over tamoxifen such as less serious side effects, which means they might be easier for you to take.  The AIs seem to have lower rates of breast cancer recurrence, which is what you want.  That said, they are significantly more expensive, so new we don’t know enough about their long term side effects, and haven’t yet shown any survival benefit.

A possible reason that they haven’t been shown to have survival benefits is that the trials to date simply haven’t been long enough for that data to happen.  Additionally, some of the studies found them superior to the degree that participants were switched off tamoxifen, meaning there wasn’t good comparison data.  But again there is a caveat – the ATAC study showed that Arimidex was superior at preventing recurrence of breast cancer, but was associated with a greater number of other cancers.

Making choosing the right medication even more complicated, there are several different drugs in the AI class and they may work in different ways.  Arimidex has become the most popular AI, for instance, but it actually may not be as effective as Femara, which is being tested in several studies right now.

Let’s go over what this all means.

The problem starts when breast cancer is detected.  Thankfully, we’re getting better and better at catching it early, which means a higher chance of stopping it from becoming even more dangerous.

First, you get surgery to remove the tumor directly.  This is important because it chops out the cancerous cells.  Unfortunately, there is the chance that the surgery won’t get rid of everything.  As such, the area is often given radiotherapy to hopefully wipe out any remaining malignant cells.

After this treatment, you may be technically tumor free – but there is a very serious risk that the cancer will come back.  Without further treatment, the risk can be as high as 45% over time.  And when it does, it does so at high rates in different parts of the body, which is particularly dangerous.

Tamoxifen – the pros

It has been used for more than 30 years as adjuvant therapy, or as an additional treatment, to help stop cancer recurring.  It’s quite effective.  One major analysis of 300,000 women showed that treatment with Tamoxifen for 5 years lowers your risk of the cancer coming back by 50%.  Translated into health benefit, the 5 year treatment lowered the death rate by an impressive 33%.

And the cons

There are a few issues with Tamoxifen.  For one, it may not do much to prevent cancer from developing after you stop taking it, which makes sense because you’re no longer taking it, but ideally would happen.  And you typically stop taking it because with time Tamoxifen highly increases your risk of developing endometrial cancer as well as blood clots.

For those reasons, while Tamoxifen is an effective and important medication, research has looked into alternative treatments, particularly the third generation of drugs in the aromatase inhibitor class.  Even a slight benefit could mean the difference to the hundreds of thousands of people treated.

What’s the difference between Tamoxifen vs Aromatase Inhibitors?

Tamoxifen blocks the effects of estrogen in the breast but, oddly enough, acts like estrogen in other parts of the body.  Aromatase inhibitors, however, knock out the production of estrogen.  This means that they are typically used in post-menopausal women.

The aromatase inhibitors directly interfere with estrogen formation in parts of the body in contrast to Tamoxifen, which only blocks estrogen in the breast while actually acting like estrogen in other parts of the body.  Because of this action, aromatase inhibitors are typically used in post-menopausal women.

Two major studies recently had some results which may indicate that some of the aromatase inhibitors are more effective than tamoxifen or may have different, and possibly less serious, side effects.  There is a general trend towards their greater use, yet, as mentioned, there is still work to be done to analyze their risks and benefits.

We will go through the various aromatase inhibitors and compare them to tamoxifen in coming posts.

Please note that the author is not a doctor.

Sources:

Current topics and perspectives on the use of aromatase inhibitors in the treatment of breast cancer

Reducing early recurrence with adjuvant aromatase inhibitors: What is the evidence?

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