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Palbociclib And Letrozole

palbociclib and letrozole


Endocrine therapy is the primary treatment option for patients with treatment-naïve estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2−) metastatic breast cancer (MBC). However, all patients eventually develop tumor progression or have primary tumor resistance to endocrine treatments. Improving response and prolonging the duration of response to endocrine-based therapy while maintaining or improving quality of life (QOL) is an important treatment goal. The addition of agents targeted to pathways contributing to resistance may improve response and delay progression, but it is critical to understand both the safety profile and the impact of these therapies on QOL [1, 2]. As such, patient-reported outcomes (PROs) are an integral component of benefit–risk assessments in the evaluation of new treatment regimens.

Clinical Trial Results

The approval was based on the results of a randomized, multicenter, open-label trial in 165 postmenopausal women with estrogen receptor–positive, HER2-negative, locally advanced or metastatic breast cancer who had not received previous systemic treatment for advanced disease. Patients were randomly assigned to receive either palbociclib (125 mg/d for 21 days, followed by 7 days off treatment) plus letrozole (2.5 mg/d continuously throughout the 28-day cycle) or letrozole alone.

Among the 165 patients, 43% had received chemotherapy and 33% had received antihormonal therapy as a neoadjuvant or adjuvant treatment; 49% of patients had no prior systemic therapy in the neoadjuvant or adjuvant setting. The majority of patients (98%) had metastatic disease.


Postmenopausal women (n = 165) with ER+, HER2-negative, advanced breast cancer who had not received any systemic treatment for their advanced disease were randomized 1:1 to receive either palbociclib in combination with letrozole or letrozole alone. Treatment continued until disease progression, unacceptable toxicity, consent withdrawal, or death. The primary endpoint was PFS. We now analyze the difference in PFS for the treatment populations by subgroups, including age, histological type, history of prior neoadjuvant/adjuvant systemic treatment, and sites of distant metastasis, using the Kaplan-Meier method. HR and 95 % CI are derived from a Cox proportional hazards regression model.


Among patients with previously untreated ER-positive, HER2-negative advanced breast cancer, palbociclib combined with letrozole resulted in significantly longer progression-free survival than that with letrozole alone, although the rates of myelotoxic effects were higher with palbociclib–letrozole. (Funded by Pfizer; PALOMA-2 number, NCT01740427.)

Similar clinical response and breast conserving surgery rates observed with letrozole/palbociclib and chemotherapy

At the interim analysis, RCB 0-I was observed in one patient in the letrozole/palbociclib arm and inclusions were stopped.

At the final analysis, local RCB 0, I, II, and III was observed in 3.8%, 3.8%, 52%, and 40.4% of patients receiving letrozole/palbociclib compared to 5.9%, 9.8%, 37.3%, 47.1% in patients on chemotherapy, respectively. Central and local RCB assessment results were identical.

The ROR score was not predictive of RCB 0/I.

The rates with neoadjuvant letrozole/palbociclib and chemotherapy were similar; the clinical objective response rates were 74.5% versus 76%, and the BCS rates were 69.2% versus 68.6%, respectively.

The final median Ki67 value was significantly lower in the letrozole/palbociclib arm; Ki67 was 3% (range 1 to 40) versus 8% (range 2 to 15) respectively (p = 0.017).

Letrozole/palbociclib demonstrated better tolerability with two serious adverse events occurring in the letrozole/palbociclib arm compared to 17 with chemotherapy (p < 0.001).

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