difference between aromasin and arimidex?

[suzan w]

can anyone tell me (in layman's terms!) what the difference in these two treatments might be?

[AlaskaAngel]

Hi Susan,

First this explanation:

"Exemestane is an irreversible, steroidal aromatase inactivator"

http://www.rxlist.com/cgi/generic3/exemest_cp.htm

the key differences there between it and the other two (anastrozole and letrozole) is that it is "irreversible" and "steroidal". To get the entire picture, talk with a good pharmacist about it.

I don't have a package insert for Aromasin handy (maybe someone else does here) but when I read it a while back it was listed as a "second-line" treatment, whereas Femara and Arimidex are listed as "first-line" treatment for breast cancer for postmenopausal women.

Arimidex has the longest history of all 3 drugs in figuring out how well it works. That doesn't mean it works better necessarily, just that they have had more time to know more about it.

Generally either Arimidex or Femara is prescribed first, even though Aromasin is sometimes better tolerated.

AlaskaAngel

[Donna]

Hi Suzan,

This was just published - the "plain english answer" is underlined and in red below. Basically the report says that there isn't enough data yet, but that Femara (letrozole) has a slight advantage over the others. Below is the report name and link in case you want to read the whole thing.

Aromatase inhibitors for treatment of advanced breast cancer in postmenopausal women
http://www.mrw.interscience.wiley.co...370/frame.html

Main results
Thirty studies were identified, twenty five of which were included in the main analysis of any AI versus any other treatment (9416 women). The pooled estimate showed a significant survival benefit for treatment with an AI over other endocrine therapies (HR 0.89, 95%CI 0.82 to 0.96). A subgroup analysis of the three commonly prescribed AIs (anastrozole, exemestane, letrozole) also showed a similar survival benefit (HR 0.88, 95%CI 0.80 to 0.96). The results for progression-free survival, clinical benefit and objective response were not statistically significant and there was statistically significant heterogeneity across types of AI. There were very limited data to compare one AI with a different AI, but these suggested an advantage for letrozole over anastrozole. All the trials of AIs used exclusively as first-line therapy were against tamoxifen. There was an advantage to treatment with AIs in terms of progression-free survival (HR 0.78, 95% CI 0.70 to 0.86) and clinical benefit (OR 0.70, 95% CI 0.51 to 0.97) but not overall survival or objective response. There was considerable heterogeneity across studies when considering clinical benefit (P = 0.001). Use of an AI as second-line therapy showed a significant benefit in terms of overall survival (HR 0.80, 95% CI 0.66 to 0.96) but not for progression-free survival (HR 1.08, 95% CI 0.89 to 1.31), clinical benefit (OR 1.00, 95% CI 0.87 to 1.14) or objective response (OR 0.96, 95% CI 0.81 to 1.14). This is difficult to interpret due to the extreme heterogeneity across AIs for progression-free survival but not the other endpoints.

AIs have a different toxicity profile to other endocrine therapies. For all AIs combined, they had similar levels of hot flushes (especially when compared to tamoxifen) and arthralgia, increased risks of nausea, diarrhoea and vomiting, but a decreased risk of vaginal bleeding and thromboembolic events compared with other endocrine therapies. A similar pattern of risks and benefits was still seen when analyses were limited to the currently most-prescribed third generation AIs.


Have a great day! Donna

[heblaj01]

Regarding the relative merits of Femara(=Letrozole) & Arimidex in terms of efficacy & side effects,studies done in the late 90's & early 2000's appeared to give a slight edge to Femara over Arimidex at least over the short to medium term.

http://clincancerres.aacrjournals.or...t/7/9/2620.pdf (2001)
Table 4 Tolerability data: indirect comparison of newer aromatase inhibitors versus megestrol acetate in second-line trials
Adverse event (%) Anastrozolea Letrozole Exemestane71 Megestrol
1 mg o.d.b 2.5 mg 25 mg 160 mg q.i.d
Headache 14 13 NA 9–13
Hot flushes 13 6 13 4–11
Nausea 18 11 9 5–23
Vomiting 8 3 NA 5–7
Diarrhea 9 6 NA 3–11
Weight gain 3 6 8e 9–17
Rash 6 6 2 3–12
Dyspnea 11 9 1 3–28
Asthenia 18 NA NA 7–20
Fatigue NA 11 8 10–22

However the long term thorough comparison of Femera & Arimidex is still awaiting since Femara among other things is affecting cortisol & as a very potent suppressor of estrogen is more likely to cause bone problems (osteoporosis, fractures...) & perhaps affect other organs such as eyes & brain more intensely than Arimidex. In addition it has been found that while Letrozole is a superior overall suppressor of estrogens compared to Arimidex (95 to 99% vs 75-85%) , it is less effective in suppressing one of the 2 main estrogens which happens to be the one which is the more cancer cell stimulating. So Arimidex may one day be found to be better than Femara for long term treatments.
These may be some of the reasons for a new large scale international clinical trial comparing the 2 drugs recently started:
http://meeting.jco.org/cgi/content/abstract/24/18_suppl/10672

Journal of Clinical Oncology, 2006 ASCO Annual Meeting Proceedings (Post-Meeting Edition).
Vol 24, No 18S (June 20 Supplement), 2006: 10672
© 2006 American Society of Clinical Oncology
The Head to Head trial: Letrozole vs anastrozole as adjuvant treatment of postmenopausal patients with node positive breast cancer

An other possible reason is competition between the manufacturers of the 2 drugs if it is funded by one of them. This already happened in one of the early head-to-head trials.

[Rozebud]

Interesting. I wonder what irriversable means?

I was given aromisin b/c my onc thought there was some preliminary evidence that it was a little less harsh on bone density than the others??

Also, what is the real difference if something is steriodal or not?

[heblaj01]

Rozebud,
In theory the word irreversible should mean that the inhibition is definitive. But I saw comments by the authors of some articles stating that the distinction between reversible & irreversible inhibitors is meaningless because tissues able to secrete estrogens (such as fatty tissues) do so quickly after the effect of aromatase inhibitors wears off.