Current treatment guidelines recommend sequential hormone therapy for patients with hormone receptor-positive (HR+) metastatic breast cancer who are not in visceral crisis and whose disease is not refractory to endocrine treatment.

Second-line fulvestrant monotherapy is a treatment option for patients in whom disease progresses after first-line palbociclib. Researchers used real-world data to evaluate the time to treatment discontinuation (TTD) of second-line fulvestrant in patients with HR+ human epidermal growth factor receptor 2-negative (HER2–) metastatic breast cancer who did (n = 88) and did not (n = 100) receive first-line palbociclib and found it was shorter in patients who received palbociclib. They presented the findings at the San Antonio Breast Cancer Symposium on December 7, 2018.

The investigators used a Flatiron Health electronic health record-derived database to identify 188 patients who progressed on first-line endocrine therapy. Patients had confirmed HR+/HER2− metastatic breast cancer between January 1, 2015, and October 31, 2017, and received second-line fulvestrant monotherapy. Researchers defined treatment discontinuation as initiation of third-line therapy, death within 60 days of the last administration of fulvestrant monotherapy, or at least 60 days between the last administration of fulvestrant and last visit date.

The overall median TTD was 114 days (95% confidence interval [CI] = 102–141); approximately half of patients receiving second-line fulvestrant discontinued treatment in less than four months. Median TTD was shorter among those who received first-line palbociclib (n = 102 days; 95% CI = 85–119) compared to those who did not (n = 127 days; 95% CI = 112–141; p = 0.006).

Compared to those who did not receive palbociclib, patients who did were more likely to

  • Be Caucasian (72.2% versus 68.0%)
  • Be younger in age (mean age = 65.0 versus 72.1 years)
  • Receive treatment at an academic institution (9.1% versus 4.0%)
  • Experience longer median duration of first-line treatment (median = 290.5 versus 211.0 days).

“Further investigation is warranted to examine whether observed results are driven by endocrine resistance or by confounding, selection, or channeling effects of new drugs,” the researchers concluded.