If my mom cannot tolerate Ribociclib, what else can she try?

Question

Hello doctor,

My mom is 59 and was diagnosed with ER+/HER2- metastatic breast cancer involving her spine. She is on Ribociclib and Letrozole and just started her second cycle. Her bloodwork showed low neutrophils (ANC 900) and rising liver enzymes.

Is this a common side effect, or could the medicines be harming her liver? The oncologist did not seem very worried, but I am concerned about the following:

If Ribociclib is not tolerated, what are the second-line options?
Also, how long do people typically respond to CDK4/6 inhibitors?
Should we consider genetic testing to personalize her treatment better?
What questions should we be asking her care team?

Please suggest.

Answer 1

Hello,

Welcome to icliniq.com.

I understand your concern.

So Ribociclib, when used with Letrozole for ER (estrogen receptors)/HER2 negative metastatic breast cancer, is a standard first-line treatment and has shown significant benefit in extending progression-free survival.

However, low neutrophil counts, like an ANC (absolute neutrophil count) of 900, and elevated liver enzymes are known and relatively common side effects of Ribociclib. The prescribing oncologist typically monitors these levels closely and will adjust the dose or pause treatment if they worsen, based on the level. While mild liver enzyme elevations are often manageable, persistent or significant increases may indicate liver irritation or toxicity, so continued monitoring is essential.

If Ribociclib is not well tolerated, alternative CDK4/6 (cyclin-dependent kinases 4 and 6) inhibitors, such as Palbociclib or Abemaciclib, will be considered, each with slightly different side effect profiles. On average, patients may respond to CDK4/6 inhibitors for two to three years, but this can vary.

Genetic testing, both tumor profiling (like next-generation sequencing) and germline testing (for inherited mutations like BRCA1/2 (breast cancer gene), can be very helpful in guiding future treatment decisions, especially for targeted therapies or clinical trials. A few questions you might ask your mother's care team include:

What is the plan if neutropenia or liver enzymes worsen?
Are dose reductions being considered?
Should we do molecular testing now to prepare for next-line therapies?
And, is she eligible for any clinical trials?

Providing her height and weight would allow for a more individualized interpretation of dosing and risk.

I hope this helps.

Thank you.