Inavolisib delays PIK3CA-mutated MBC progression by almost eight months | ASCO 2024

Background

Endocrine therapy is the main drug treatment for hormone receptor-positive, HER2-negative breast cancer. If the cancer spreads, doctors add targeted therapy in the form of a CDK 4/6 inhibitor to the endocrine therapy for a more powerful effect. Fulvestrant (Faslodex) is hormone therapy commonly given to postmenopausal women. Palbociclib (Ibrance) was the first CDK 4/6 inhibitor approved by the FDA to treat breast cancer. In combination, they are a common first treatment for advanced or metastatic hormone receptor-positive, HER2-negative breast cancer.

Inavolisib works by targeting PIK3CA mutations in breast cancer cells. Approximately 40% of hormone receptor--positive metastatic breast cancers test positive for a PIK3CA mutation. Together, the three drugs create a stronger offense against cancer, interfering with cancer growth in three different ways.

Results

People who took inavolisib went more than twice as long without cancer growth or spread than those who did not (15 months versus 7.3 months). The phase III randomized, double-blind clinical trial INAVO120 included 325 people. All had hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer that tested positive for the PIK3CA mutation.

This study looked at the three-drug combination (inavolisib, fulvestrant, and palbociclib) for cancers that had spread on hormone therapy alone. All three drugs were given at full dose. Inavolisib and palbociclib are pill you can take at home. Fulvestrant is a shot to a muscle in the buttocks and is given in a doctor’s office.

Inavolisib is generally well tolerated, with milder side effects than other drugs that target the PIK3CA mutation. It can cause diarrhea, mouth sores, and skin rash. The presenting doctors emphasized the importance of reporting side effects right away. Side effects that were managed in the first month of treatment went away more quickly.

This study also looked at quality of life. Participants in the inavolisib group also went longer (over a year) without cancer-related pain getting worse. They were also less bothered in general by the drug combination. Most answered “not at all” or “a little bit” when asked how bothered they were by the side effects of treatment in the past week.

What does this mean for you?

This three-drug combination is likely to become another standard treatment option for hormone receptor-positive, HER2-negative advanced or metastatic breast cancer. Inavolisib does not yet have FDA approval but was recently granted breakthrough therapy designation. It is expected to be approved in November 2024.

Other treatments that target metastatic breast cancer with a PIK3CA mutation are alpelisib (Piqray) and capivasertib (Truqap).

A key takeaway from this report is the importance of biomarker testing for everyone with advanced or metastatic breast cancer. One test may be enough to expand your treatment options. Ask your doctor if the cancer was already tested for biomarkers, including PIK3CA mutations. If not, ask about testing options. If the tumor tests positive for a PIK3CA mutation, inavolisib may be an option for you.

This drug combination is one of a few new drug therapies available to people with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer. Discuss your options with your healthcare team, including:

• Costs and insurance coverage for any treatment you’re considering
• Possible side effects; the combination of inavolisib, fulvestrant, and palbociclib had relatively mild side effects that were managed well when reported right away

No matter what your treatment plan is, always let your healthcare team know about any side effects or other changes you notice.