Just off the top of my head, my recollection is that the trials of endocrine treatments show a relative reduction in recurrences in the range of 30-40%. The higher one's risk is, the more the (absolute) benefit. Also, the higher the ER/PR of the cancer is, the more the benefit.
So for example, if your risk of recurrence after surgery and chemo/anti-HER2 agent is small, say 10% -- the absolute benefit of endocrine therapy (using the 30% reduction figure) would be about 3.3% (1/3 of 10%), bringing your risk down to 6-7% (10% minus 3.3%). On the other hand, if your risk of recurrence is higher, say 60%, then endocrine treatment would add a much bigger benefit, bringing your risk down to about 40% (1/3 of 60% = 20% and 60% minus 20% = 40%).
In addition, there's the spectrum of ER/PR positivity to consider. Those with lower levels of ERPR probably get less benefit from endocrine treatment (and vice versa -- high ERPR levels in the cancer probably benefit more), although this is harder to pin down with actual numbers.
And for those who had lumpectomy or a single mastectomy (iow, those with breasts), these drugs also reduce the risk of a new primary.
These figures are for very large groups of women, with diverse details of diagnosis. They are used to guide treatment decisions but because each person and each cancer is different, the figures are not super-accurate for any one individual.
Here's an article that starts out with discussions (and tables) about the early trials of Tamoxifen and ovarian suppression (and has some recurrence reduction figures). Then it moves on to the more recent studies that try to tweak which agent offers the most benefit, and what is the best duration of treatment, which are the questions being asked today.
Each person will base their decision about endocrine therapy on several factors, including risk of recurrence and experience with side effects. If side effects are too much, many find that switching to a different drug, even within the same class of drugs (so for example switching from the AI Arimidex to the AI Letrozole) may decrease side effects. The side effect profile of Tamoxifen is a bit different so if you can't find an AI that works for you, switching to Tamoxifen is also an option.
Hadit, if you don't feel that you can ask your onc for explanations and information, it would be worth trying a visit with a different oncologist, even within the same group. We all want a competent oncologist directing our care, but we also deserve one we feel we can talk to. And that last bit is more of a personality-fit issue than a competence one, so who is "good" in that way will vary for each of us, and you won't know who is a good fit for you without trying out other providers. Good luck!
Debbie Laxague