338TiP CAPItello-292: A phase 1b/3 study of capivasertib, palbociclib and fulvestrant versus placebo, palbociclib and fulvestrant in HR+/HER2− advanced breast cancer

Phase I/Ib Trial of Inavolisib Plus Palbociclib and Endocrine Therapy for PIK3CA-Mutated, Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Advanced or Metastatic Breast Cancer

PURPOSE

To investigate the safety, tolerability, pharmacokinetics (PK), and preliminary antitumor activity of inavolisib, a potent and selective small-molecule inhibitor of p110α that promotes the degradation of mutated p110α, in combination with palbociclib and endocrine therapy (ET), in a phase I/Ib study in patients with PIK3CA-mutated, hormone receptor-positive/human epidermal growth factor receptor 2-negative locally advanced/metastatic breast cancer (ClinicalTrials.gov identifier: NCT03006172).

METHODS

Women ≥18 years of age received inavolisib, palbociclib, and letrozole (Inavo + Palbo + Letro arm) or fulvestrant (Inavo + Palbo + Fulv arm) until unacceptable toxicity or disease progression. The primary objective was to evaluate safety or tolerability.

RESULTS

Fifty-three patients were included, 33 in the Inavo + Palbo + Letro arm and 20 in the Inavo + Palbo + Fulv arm. Median duration of inavolisib treatment was 15.7 and 20.8 months (cutoff: March 27, 2023), respectively. Treatment-related adverse events (TRAEs) occurred in all patients; the most frequent were stomatitis, hyperglycemia, and diarrhea; grade ≥3 any TRAE rates were 87.9% and 85.0%; 6.1% and 10.0% discontinued any treatment due to TRAEs in the Inavo + Palbo + Letro and Inavo + Palbo + Fulv arms, respectively. No PK drug-drug interactions (DDIs) were observed among the study treatments when administered. Confirmed objective response rates were 52.0% and 40.0% in patients with measurable disease, and median progression-free survival was 23.3 and 35.0 months in the Inavo + Palbo + Letro and Inavo + Palbo + Fulv arms, respectively. Available paired pre- and on-treatment tumor tissue and circulating tumor DNA analyses confirmed the effects of study treatment on pharmacodynamic and pathophysiologic biomarkers of response.

CONCLUSION

Inavolisib plus palbociclib and ET demonstrated a manageable safety profile, lack of DDIs, and promising preliminary antitumor activity.

At a crossroads: how to translate the roles of PI3K in oncogenic and metabolic signalling into improvements in cancer therapy

Numerous agents targeting various phosphatidylinositol 3-kinase (PI3K) pathway components, including PI3K, AKT and mTOR, have been tested in oncology clinical trials, resulting in regulatory approvals for the treatment of selected patients with breast cancer, certain other solid tumours or particular haematological malignancies. However, given the prominence of PI3K signalling in cancer and the crucial role of this pathway in linking cancer growth with metabolism, these clinical results could arguably be improved upon. In this Review, we discuss past and present efforts to overcome the somewhat limited clinical efficacy of PI3Kα pathway inhibitors, including optimization of inhibitor specificity, patient selection and biomarkers across cancer types, with a focus on breast cancer, as well as identification and abrogation of signalling-related and metabolic mechanisms of resistance, and interventions to improve management of prohibitive adverse events. We highlight the advantages and limitations of laboratory-based model systems used to study the PI3K pathway, and propose technologies and experimental inquiries to guide the future clinical deployment of PI3K pathway inhibitors in the treatment of cancer.