There has been a lot of debate about how to prevent cancer from coming back in post-menopausal women after initial treatment.  We discussed in our comparison of Tamoxifen with aromatase inhibitors the debate in general, and now will analyze Tamoxifen vs Anastrozole, brand name Arimidex, directly.

The data seems to say this: Arimidex is more effective than tamoxifen in preventing breast cancer from coming back.  And it may have different, less serious side effects.  But it does not necessarily increase your lifespan compared to tamoxifen.

(That said, please see the past post for an analysis of why that may be so despite what seems to be superior breast cancer prevention.)

What the studies say: ATAC

This study set out to compare Anastrozole, brand name Arimidex, to Tamoxifen Alone or in Combination (hence, “ATAC,” an aggressive name for a study trying to shake things up.)  The question was, would treatment with anastrozole alone be better than tamoxifen alone, or would they work best in combination?

The results have been reported by some as a strong indication of superiority for anastrozole.  Arimidex, for instance, had significantly longer time to develop new cancer as compared to Tamoxifen.  As one site puts it, anastrozole increased disease free survival by 10%, time to relapse by 20%, and reduced cancer spread by 14%.

There’s more.  In terms of side effects, anastrozole may have a significantly lower level than tamoxifen of serious issues like cerbrovascular, thromboembolic and endometrial cancer incidents.

But there is an important caveat.


While the form of disease progression seems to be significantly better with anastrozole than tamoxifen, the study did not show any ultimate difference in survival rates.  And anastrozole may have a higher rate of ischemic heart disease as well as a higher rate of unrelated, new cancers like lung and colorectal cancer, in general.  It had 54 new cancers as compared to 38 new ones for tamoxifen.

The Italian Tamoxifen Arimidex Trial

This study looked at 448 estrogen receptor positive, node positive post menopausal women.  (The estrogen/node receptor status will be discussed further in other posts.)  In that test, tamoxifen was either taken for 5 years or for 2-3 years then switched to Arimidex.

The results?  At 64 months, those who switched to arimidex had a better rate of event-free survival as well as relapse free survival.  Which is very promising.  Yet once again, there was no overall improvement in mortality.

Australian Breast and Colorectal Cancer Study Group

This study also looked at people taking tamoxifen for 5 years, or those who take it for several than switch to Arimidex.  A “censored” version of results that wasn’t official showed no advantage in cancer recurrence for Arimidex but a slight improvement in overall survival.

This is interesting because it’s the opposite of the other studies which have various benefits but no end result survival benefit.

Please note that the author is not a doctor.


3 Phase 3 Trials of Aromatase Inhibitors for Breast Cancer Prevention
Switching from tamoxifen to aromatase inhibitors for adjuvant endocrine therapy in postmenopausal patients with early breast cancer