When to start Aromatase Inhibitors?
I am currently in treatment for triple positive breast cancer. I had surgery in June 2024 followed by 12 weeks of chemotherapy with paclitaxel and trastuzumab, then followed on with the trastuzumab every three weeks which will continue until July 2025. I just started daily radiation and have 12 more treatments. My oncologist now wants me to start on Letrozole. I feel it is too much. How can I tell which side effects are from which treatment? I will make my decision based on what my body is telling me it can handle. But I like to be informed. I cannot find any information on when the best time is to start on an AI. Why not wait until other treatments have ended? Is there any advantage to starting on an AI while receiving targeted immunotherapy? I can't find any information.
Comments
-
Hi @mgradie, Triple positive breast cancer requires more treatment than other types because there are two drivers of cancer, estrogen and human epidermal growth factor receptor 2. Letrozole and other hormone blockers deplete estrogen in your body and trastuzumab binds to HER2 proteins inactivating them. Both prevent the cancer from growing. If you only treat one of the drivers the other one will continue to help the cancer grow. It's kind of like going to the doctor with a severe respiratory infection and testing positive for both flu and bacterial pneumonia. You will be prescribed tamiflu and an antibiotic since there are two different causes with different treatments. Here is a link to a technical paper that explains the rationale. It is old (2003) but using both treatments has been standard of care for a long time.
https://www.annalsofoncology.org/article/S0923-7534(19)64238-9/fulltext
Whatever the cause side effects tend to be treated by symptoms. Going back to the respiratory infection analogy, a bad cough caused by either or both would be treated by a prescription cough suppressant. If letrozole causes new side effects there are treatments available. There are also two other AIs and tamoxifen which works differently by binding to the estrogen receptors. Many people tolerate one of these more easily than the other.
Have a discussion with your oncologist about your side effect worries to find out what can be done for you if you happen to develop them. All the best for successfully completing your treatment.
0 -
Thanks @maggie15. I think I didn't state my question my question well. It isn't really whether there is an advantage to combining trastuzumab with an Aromatase Inhibitor. That is well established. The question really is if there is an optimal time to start on AI. I am interested in other people's experience. Is there any problem with waiting until after I complete my radiation?
I am completely familiar with the treatment, the scientific literature, the underlying physiological mechanisms, and I have no problem with following through with the treatment or speaking with my oncologist about my treatment.
0 -
Hi @mgradie, Sorry for the misinterpretation. There have been a few studies which have shown starting an AI before or after radiation is equally effective and the same in terms of possible side effects. Tamoxifen should not be taken until after radiation since if taken concurrently it is more likely for fibrosis to occur. It seems that if you would prefer to wait until after rads it is only a short delay.
There are no guarantees since I ended up with pulmonary fibrosis from rads taking neither med. Unbeknownst to me I had subclinical ILD making me susceptible to some very rare radiation SEs. Whatever you decide to do I hope your radiation treatment goes well.
0 -
Mgradie, I am also triple positive. I started anastrozole right after surgery, at the same time I started Kadcyla. I did paclitaxel with trastuzamab and perjeta before surgery but did not get pCR. Kadcyla is trastuzumab with emtansine, so I was taking anastrozole at the same time as trastuzumab. I did Kadcyla for 10 1/2 months and am now continuing with anastrozole daily and Zometa every 6 months. My MO definitely did not want me to wait.
0
