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Dec 17, 2019 10:07AM
From the standpoint of tolerance, which is best depends on the person taking it.
If you read the board, you'll find that there are people who started with Letrozole (Femara or generic) or with Anastrozole (Arimidex or generic) or with Exemestane (Aromasin or generic) and did well. Then there are others who started with any of the three, had quality of life side effects, switched to one of the others and did well. There are some people will tolerate any of the AIs well, and other people who will have trouble tolerating any of them.
For those for take the generic versions, sometimes one brand of generic is more tolerable than another brand of generic, for the very same drug.
From the standpoint of side effects, again it depends very much on the individual, but here is a comparison from BCO:
And here are comparisons of Anastrozole vs. Letrozole, and one of Aromasin vs. Anastrozole .
From the standpoint of effectiveness and toxicity, the results seem to vary depending on the study. Generally all 3 AIs perform about the same.
Here are a number of studies that have compared the effectiveness of the AIs:
Adjuvant anastrozole versus exemestane versus letrozole, upfront or after 2 years of tamoxifen, in endocrine-sensitive breast cancer (FATA-GIM3): a randomised, phase 3 trial (2018)
- "5-year disease-free survival was 90·0% (95% CI 87·9–91·7) with anastrozole (124 events), 88·0% (85·8–89·9) with exemestane (148 events), and 89·4% (87·3 to 91·1) with letrozole (129 events; p=0·24). No unexpected serious adverse reactions or treatment-related deaths occurred."
Do all aromatase inhibitors have similar efficacy and safety? (2017)
- "Letrozole is a more potent inhibitor of aromatase than anastrozole at their conventionally used doses, and leads to more complete inhibition of whole-body aromatase. Geisler et al. reported that mean percentage aromatase inhibition with anastrozole was 97.1%, whereas more than 99.1% suppression of aromatase enzyme was observed with letrozole in standard treatment doses"
- "In a randomized Phase III MA.27 trial (NCT00066573), the efficacy of
steroidal aromatase inhibitor exemestane and nonsteroidal aromatase
inhibitor anastrozole for 5 years in the adjuvant hormonal treatment of
hormone receptor-positive postmenopausal early breast cancer was
Total of 7576 patients were enrolled in this first comparison of
steroidal and nonsteroidal classes of aromatase inhibitors trial, and
the primary outcome 4-year event-free survival (EFS) rates were similar:
91% for exemestane and 91.2% for anastrozole in the initial adjuvant
therapy of hormone receptor-positive breast cancer with a median
4.1-year follow-up (HR: 1.02; 95% CI: 0.87–1.18; p = 0.85). In a recent
published randomized Phase III Femara Versus Anastrozole Clinical
Evaluation (FACE) trial (NCT00248170), Smith et al. compared the
efficacy and safety of adjuvant letrozole and anastrozole in
postmenopausal patients with hormone receptor and node-positive early
breast cancer .
A total of 4136 patients were randomized and 5-year estimated
disease-free survival (DFS) rates were 84.9 and 82.9% for letrozole and
anastrozole arms, respectively (HR: 0.93; 95% CI: 0.80–1.07; p = 0.31)."
No Efficacy Difference Between Adjuvant Letrozole and Anastrozole in Postmenopausal Women With Early Breast Cancer (2017)
- "The 5-year estimated disease-free survival rate was 84.9% in the letrozole group vs 82.9% in the anastrozole group.....The 5-year estimated overall survival rate was 89.9% vs 89.2%"
- "The most common adverse events of any grade in the
letrozole vs anastrozole groups were arthralgia (48% vs 48%), hot
flushes (33% vs 32%), fatigue (17% vs 17%), osteoporosis (11% vs 11%),
myalgia (11% vs 10%), and back pain (10% vs 9%). The most common grade 3
or 4 adverse events were arthralgia (3.9% vs 3.3%), hypertension (1.2%
vs 1.0%), hot flushes (0.8% vs 0.4%), myalgia (0.8% vs 0.7%), dyspnea
(0.8% vs 0.5%), and depression (0.8% vs 0.6%)."
- "Adverse events led to discontinuation of treatment in 15.1% vs 14.3% of
patients and dose interruption or reduction in 8.2% vs 7.7%. Serious
adverse events considered related to treatment occurred in 2.6% vs 2.3%.
Death occurred in 2.0% vs 2.2% of patients; causes other than disease
progression included cardiac failure (six vs two patients), pulmonary
embolism (two vs four patients), and chronic obstructive pulmonary
disease (one vs four patients)."
Differences between the non-steroidal aromatase inhibitors anastrozole and letrozole – of clinical importance? (2011)
- "In addition to being the most potent non-steroidal AI, letrozole is the
only AI that has demonstrated superior efficacy in both the neoadjuvant
and adjuvant settings compared with tamoxifen. A significant reduction
of early DM in the adjuvant setting has been shown with letrozole, and a
survival benefit is emerging with longer follow-up in the BIG 1–98
trial. In contrast, 100-month survival data from the ATAC trial do not
demonstrate an OS benefit for anastrozole vs tamoxifen."
What it comes down to is that different MOs have different preferences, possibly depending on which study they read last or which study sticks in their mind most. There is really nothing out there that says that one is any better than the others, or that one will be more easily tolerated. It's all a question of how your body reacts to one vs. another.
“No power so effectually robs the mind of all its powers of acting and reasoning as fear.” Edmund Burke