OBJECTIVES

Randomized controlled trials and published guidelines recommend endocrine therapy, specifically cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i) in combination with either aromatase inhibitors or fulvestrant, as first-line (1L) therapy for hormone receptor-positive (HR+) human epidermal receptor2 negative (HER2-) metastatic breast cancer (mBC). Chemotherapy is reserved for patients in visceral crisis. We aimed to understand the use of 1L chemotherapy in the treatment of HR+/HER2- mBC in the U.S. post-approval of the first CDK 4/6i palbociclib in 2015.

METHODS

Female HR+/HER2- patients diagnosed with mBC (at least one non-diagnostic inpatient/two outpatient claims for breast cancer and one claim for lymph node/distant metastatic disease) initiating 1L treatment between 01/01/2015 and 10/31/2018 were identified in the Symphony Health administrative claims database. Regimes received in 1L were categorized as: single-agent chemotherapy (saChemo), combination chemotherapy (cChemo), and hormonal/targeted (H/T). Patient demographics, frequency of use of agents, comorbidities (Charlson components) at 1L initiation, and the proportion of patients who had not initiated second-line (2L) therapy (proxy for progression-free survival) at 6 months from 1L start of treatment (Kaplan-Meier method) were assessed.

RESULTS

4317 HR+/HER- patients were identified. 1L treatment patterns/mean age: saChemo 18%/64yrs, cChemo 21%/61yrs, H/T 61%/67yrs. Comorbidities >2: saChem=6%, cChemo=4%, H/T=6%. Visceral metastasis: saChemo=23%, cChemo=19%, H/T=58%. The top 3 most frequent saChemo: capecitabine=12%, paclitaxel=11%, nab-paclitaxel=11%; cChemo: cyclophosphamide/doxorubicin=23%, cyclophosphamide/docetaxel=9%, carboplatin/paclitaxel=4%.; H/T: anastrozole=25%, letrozole=23%, fulvestrant=13%. 6-month proportion of patients not initiating 2L, saChemo: paclitaxel=94%, capecitabine=76%, docetaxel=60%; cChemo: carboplatin/nab-paclitaxel=86%, carboplatin/paclitaxel=84%, carboplatin/docetaxel=74%; H/T: letrozole/palbociclib=89%, letrozole=84%, anastrozole=82%.

CONCLUSIONS

Endocrine therapy is recommended by the NCCN guidelines as the treatment of choice for HR+/HER2- patients. However, chemotherapy still constitutes >40% of 1L choices since the introduction of CDK4/6i. More alarming is the continued use of cChemo for these patients. Further long term follow-up is needed to understand median time to next treatment (proxy for progression-free survival).