Background and importance The inhibitor of cyclin dependent kinases 4 and 6, palbociclib, was a major advance in the treatment of metastatic breast cancer.
Aim and objectives To describe the effectiveness and incidence of neutropenia with palbociclib in clinical practice.
Material and methods A retrospective study was conducted in patients with metastatic or locally advanced breast cancer treated with palbociclib on any line in a tertiary hospital between July 2016 and August 2020. Demographic variables were collected: start and end date of the drug, concomitant hormonal treatment and treatment with denosumab. The presence of neutropenia was assessed before the start, on day 15 of the first cycle and with each reduction.
Results 58 patients were included with a median age at the start of palbociclib treatment of 59.0 years (33–87); the median cycle was 9 (2–34). 50% were on concomitant treatment with fulvestrant, 43.1% with letrozole, 3.4% with goserelin, 1.7% with anastrozole and 1.7% with exemestane. 44.8% of patients were treated with denosumab for bone metastases. The average neutrophil count was reduced by 52.9% from the beginning to the middle of the first cycle, with neutropenia appearing in 69.0% of patients (1.7% grade 4; 22.4% grade 3; 24.2% grade 2, 20.7% grade 1). 44.8% (26) had a first level reduction to 100 mg, with neutropenia appearing in 92.3% of these (15.4% grade 4; 61.5% grade 3; 15.4% grade 2). 46.2% of the previous patients (12) required a further reduction to 75 mg, with neutropenia appearing in 91.6% (58.3% grade 3; 25% grade 2; 8.3% grade 1). The average progression free survival was 17.6 (±1.8) months. Overall survival averaged 25.7 (±1.3) months. Patients with dose reductions were not more likely to progress (p=0.196). 51.7% received palbociclib as firstline, 32.8% as secondline and 15.5% as successive lines of treatment.
Conclusion and relevance Haematological toxicity in the form of neutropenia was frequent, from the first cycle, and remained despite successive dose reductions; reductions were needed in almost half of the patients. However, these dose reductions were not associated with an increased risk of progression. Bone metastasis is very common in metastatic or locally advanced breast cancer. Since the authorisation for firstline use (PALOMA-2) it has become a standard of treatment for metastatic or locally advanced breast cancer.
Conflict of interest No conflict of interest
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