Excellent question! Unfortunately, the short answer is no one knows what the benefit vs the risks of taking femara (letrozole) indefinitely are.
Now the long answer: I believe, but I may be wrong, that the trial you are referring to is the famous MA-17 trial in which women over 50 years were randomly assigned to either 5 years of placebo or 5 years of letrozole after finishing 5 years of tamoxifen.
That same trial is also trying to answer the risk/benefit question of extended femara: first, an extension of the MA 17 trial is currently on going where women who had completed 5 years of letrozole have been randomized to either receive another 5 years of letrozole versus placebo. Preliminary results indicate that there may be additional survival benefit from extended femara.
That said, even though the results of the extended study is encouraging, that may or may not apply to your case. Since these women did not stop taking hormonal therapy but are receiving it for 15 years.
On the other hand, that same trial is also trying to assess the health hazards of femara, which is a relatively new drug when compared to tamoxifen. In particular a subset of the MA 17 patients were studied in a companion trial for the impact of femara on bone density. It was clear that even after 2 years of femara there was a significant decrease in bone density. This added to the normal fact, that women after 50 are more likely to develop osteoporosis makes this a significant issue. However, I am sure, however, that is being monitored by your physician.
Apparently, it looks like femara extension is relatively safe with a few precautions. However, like I said, its a relatively new drug and we have to wait before we can tell exactly what the hazards are.
In contrast, Tamoxifen has been around since the 1970's we know that extended tamoxifen beyond 5 years does not offer benefit and is associated with an increased incidence of uterine cancers (up to 4 times the risk in normal population). Even in this case, which seems rather obvious at first, there are studies examining whether there is a subset of women which high risk disease that may benefit from extended tamoxifen beyond 5 years. I believe there are two trials examining this issue (ATLAS, ATOM).
Your doctor would be the best person to make a decision in an area where there are no clear answers. He should weigh the benefits versus the risks and compare it to your risk for recurrence. If you are not at high risk for disease recurrence, I would say that the benefit, if any, is minimal at this stage.
I have included the reference for the MA 17 extension trial below for your reference.
1. Ingle JN; Tu D; Pater JL; Martino S; Robert NJ; Muss HB; Piccart MJ; Castiglione M; Shepherd LE; Pritchard KI; Livingston RB; Davidson NE; Norton L; Perez EA; Abrams JS; Cameron DA; Palmer MJ; Goss PE. Duration of letrozole treatment and outcomes in the placebo-controlled NCIC CTG MA.17 extended adjuvant therapy trial. Breast Cancer Res Treat. 2006 Oct;99(3):295-300. Epub 2006 Mar 16.
Dr. Tamer Fouad, MD
MB, BCh, MSc Internal Medicine.
Consultant of Hematology - Oncology.