The combination of capivasertib (Truqap) and fulvestrant is emerging as a valuable treatment option for patients with PIK3CA-altered metastatic breast cancer, offering improved progression-free survival (PFS) compared to fulvestrant alone. This was highlighted in the phase 3 CAPItello-291 trial, which evaluated the efficacy and safety of this combination in patients who had progressed on or after first-line endocrine therapy.
The trial included patients with metastatic breast cancer who had received two or fewer prior lines of endocrine therapy and one or fewer lines of chemotherapy. Patients were randomized to receive either capivasertib plus fulvestrant or placebo plus fulvestrant. A key aspect of the trial was the assessment of PFS in both the overall population and in patients with PIK3CA, AKT, or PTEN alterations.
Efficacy and Outcomes
In the overall population, the median PFS with capivasertib plus fulvestrant was 7.2 months compared to 3.6 months with fulvestrant alone (HR, 0.60; 95% CI, 0.51-0.71; 2-sided P < .001). Notably, in patients with AKT/PIK3CA/PTEN-altered tumors, the median PFS was 7.3 months versus 3.1 months, respectively (HR, 0.50; 95% CI, 0.38-0.65; 2-sided P < .001).
According to Dr. Ursa Brown-Glaberman, Associate Professor at the University of New Mexico School of Medicine, "In the overall population, the median PFS with capivasertib plus fulvestrant was 7.2 months vs 3.6 months with just fulvestrant." She also noted a trend toward improved overall survival (OS) with the addition of capivasertib, although the OS data were still immature at the time of analysis.
Comparison with Alpelisib
Alpelisib (Piqray) is another PI3K inhibitor approved for PIK3CA-mutated breast cancer. While cross-trial comparisons are limited, data from the BYLieve trial suggest comparable PFS outcomes to capivasertib in similar patient populations. However, alpelisib is associated with a higher incidence of grade 3 hyperglycemia (23% to 36%) compared to capivasertib (2.3%).
"Anyone who has used alpelisib knows that the hyperglycemia can be challenging," Dr. Brown-Glaberman stated. "In terms of grade 3 hyperglycemia, it ranges between 23% and 36% with alpelisib vs 2.3% with capivasertib."
Dosing and Tolerability
Capivasertib is administered on a 4-days-on, 3-days-off schedule, which may pose adherence challenges for some patients. Strategies such as pill box organizers and smart pill bottles can help improve adherence. In contrast, alpelisib is administered daily.
Dr. Brown-Glaberman emphasizes the importance of patient education and monitoring: "Using a pill box organizer is critical... Right now, we’re using Pillsy bottles where it records every time they take it."
Sequencing Strategies
The optimal sequencing of targeted therapies in PIK3CA-mutated breast cancer remains an area of active investigation. Dr. Brown-Glaberman suggests considering capivasertib before elacestrant (Orserdu) in patients with better performance status due to its potentially more favorable toxicity profile.
Clinical Implications
The CAPItello-291 trial supports the use of capivasertib plus fulvestrant as a valuable option for patients with PIK3CA-altered metastatic breast cancer, particularly those who have progressed on prior endocrine therapy. Its manageable toxicity profile, especially regarding hyperglycemia, may make it a preferred choice for some patients compared to other PI3K inhibitors.
