The results of the phase II PALOMA-1/TRIO-18 trial were recently reported in The Lancet Oncology and suggest that the addition of Ibrance® (palbociclib) to Femara® (letrozole) delayed the time to cancer progression when used as first-line treatment for advanced breast cancer in postmenopausal women with estrogen receptor (ER)–positive/human epidermal growth factor receptor 2 (HER2)-negative disease.

Ibrance® is a kinase inhibitor now approved for use in combination with Femara® for the treatment of postmenopausal women with ER-positive, (HER2)-negative advanced breast cancer as initial endocrine-based therapy for their metastatic disease.

In PALOMA study, post menopausal women with advanced ER+/HER2-  breast cancer were enrolled in two sequential groups; one without, and one with amplification of cyclin D1 (CCND1), loss of p16 (INK4A or CDKN2A), or both. All patients were treated with continuous Femara® with or without Ibrance®  in 28-day cycles and their outcomes directly compared.

The study population is now on average approximately 29 months from initiation of treatment and overall 43% of women responded to treatment with the Femara®-Ibrance® combination compared to only 33% of those treated with Femara® alone.  On average, individuals treated with the combination experienced a doubling in survival without evidence of cancer progression.  The addition of Ibrance® improved the time to cancer progression to 20.2 months compared to only 10.2 months for those treated with Femara® alone.

On average, women treated with Ibrance® survived 37. 5 months compared to 33.3 months for those treated with Femara® alone. Bone marrow toxicity was the most common side effect in the Ibrance®/Femara® group and manifested as low blood counts fatigue. The trial is ongoing and a more mature analysis is expected to be published at a future date.

The study authors concluded that the addition of Ibrance® to Femara® significantly improved progression-free survival in women with advanced estrogen receptor-positive and HER2-negative breast cancer. A phase 3 clinical study is currently underway with the goal of confirming these observations.

Reference: Finn R, Crown J, Lang I, et al. The cyclin-dependent kinase 4/6 inhibitor palbociclib in combination with letrozole versus letrozole alone as first-line treatment of estrogen receptor-positive, HER2-negative, advanced breast cancer (PALOMA-1/TRIO-18): a randomised phase 2 study. The Lancet Oncology, Vol 16, No. 1, p25-35, January, 2015.

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