[Becky]

As most of you know, there are 3 aromatase inhibitors (AI) on the market. They include Arimidex, Femara and Aromosin. All three products prevent a biochemical reaction in the body. This reaction converts androgens to estrogen. In order to do this reaction, the body needs the catalyst, aromatase. These drugs prevent the action of aromatase, therefore, no production of estrogen. The production of estrogen in this manner is done in the adrenal glands and fat cells. Production of estrogen in the ovaries is different and this is why one needs to be postmenopausal to take an AI.



Which is better? Well, the jury is still out on that. There is an ongoing trial comparing the three drugs to each other. Obviously, everyone will be more interested in the long term results which won’t be there for quite some time but at least the study is going.



Arimidex and Femara work the same way in the body and inhibit aromatase in the same non-steroidal way in the exact same place in the biochemical reaction. Aromosin has a steroidal action and inhibits aromatase in a different step of the biochemical reaction. Because of this, there could be different side effects between the Arimidex/Femara versus Aromosin. For example, there is a possibility of developing high cholesterol on Arimidex or Femara but not as likely using Aromosin. So, sometimes when I see that some women are having joint pain on Arimidex, I will recommend trying Aromosin before I would recommend Femara just because Arimidex and Femara work the same way. That said – why are the drugs recommended the way they are. Most of it comes down to what trials (and the results of those trials) have been completed. We all know the oncs love data before prescribing drugs, chemo, targeted therapies…



The trials were as follows (and I may have missed some)

• 5 years of Arimidex versus 5 years of Tamoxifen. This trial showed that Arimidex works significantly better than Tamoxifen in postmenopausal women.
• 2 years of Tamoxifen followed by either 3 more years of Tamoxifen or 3 years of Arimidex. This study showed that switching to an Arimidex after 2 years of Tamoxifen was much better than staying on Tamoxifen.
• Same as #2 but using Aromosin instead – same results as Arimidex. Switching is better.
• 5 years of Tamoxifen then half the women got 5 years of Femara and the other half was observed. The Femara half did better.

This is why Arimidex is prescribed more often than Femara as a first line therapy. It is because Arimidex has been trialed as a first line drug and the others have not been yet (except for the ongoing trial comparing the 3 drugs head to head of which there are no results). Femara is only FDA approved (so far) to be used after completing 5 years of Tamoxifen. Aromosin is only approved to be used after at least 2 years of Tamoxifen. It does NOT mean they don’t work otherwise or work better or if you are experiencing bad side effects on one that you shouldn’t switch to another one. It also does not say which is better as a first line treatment in non metastatic breast cancer. (The trial should shred light on that). However, in metastatic bc, there are some studies with bone mets (2) that have shown that Femara seems to be slightly more effective (but not statistically so and the study # of participating women was small). Theorectically, each should work in the first line setting (meaning that they should work better than having to use Tamoxifen first but Arimidex has been proven to work better than Tamoxifen without having to use Tamoxifen first).

So, that’s my story and I’m stickin” to it.

Kind regards, Becky