Abstract P1-16-10: Treatment patterns and outcomes of different subtypes of metastatic breast cancer patients in a Swedish real world setting with a focus on HER2-/HR+ subtype
Authors: Lindman H , Szilcz M , Freilich J , Carlqvist P , Vertuani S , Anell B , Holm B 
Published: May 2019

Introduction: The most frequent molecular subtype of metastatic breast cancer (MBC) is the HER2-/HR+ subtype. While there are several treatments available for HER2-/HR+ MBC patients, there is limited knowledge about how patients are treated in a real world setting. In this retrospective study, the aim was to describe the duration of four initial treatment lines, treatment patterns and outcomes in MBC subtypes, with a focus on the HER2-/HR+ subtype.

Methods: The population is a cohort of 370 MBC patients diagnosed during '09-´16 in Uppsala County, Sweden. Data were collected from a regional breast cancer registry which included medical records. The subtypes were HER2-/HR+(59%); HER2+/HR+(12%); HER2+/HR-(7%) and HER2-/HR-(12%) based on immunohistochemistry (IHC) and in situ hybridization (ISH) tests, 11% of records had missing data on subtypes. Kaplan-Meier estimates were used to model duration of treatment line, progression-free survival (PFS) and overall survival (OS). Cox proportional hazard models were used to test the association, expressed in hazard ratios (HR), between the subtypes and PFS and OS.

Results: The median PFS and OS of HER2-/HR+ subtype were 10.6 and 36.7 months, respectively. Compared to the HER2-/HR+ patients, a statistically significant difference was found for HER2-/HR- patients in terms of PFS (HR: 2.1; p-value&lt;0.001) and OS (HR: 3.6; p-value&lt;0.01), indicating a worse prognosis. HER2+/HR+ and HER2+/HR-patients had similar PFS and OS results to HER2-/HR+ patients.

A statistically significant association was found between HR+ expression and OS (HR: 0.5; p-value&lt;0.001) and not between HER2+ expression and OS (HR: 1.0; p-value 0.79 ).

The median duration of treatment decreased with increasing treatment lines; HER2-/HR+ patients' first-line treatment lasted 7.2, second-line 5.5, third-line 4.7 and fourth-line 4.4 months. The proportion of chemotherapy increased with the number of treatment lines: 32%, 38%, 46% and 59% for first to fourth line, respectively.

The ten most used drugs of HER2-/HR+ cohort are summarized in Table 1. In total, endocrine therapy was given during 66% of the total treatment duration.

Table 1:Ten most used drugs of HER2-/HR+N=197Patient-years (sum of treatment durations)Relative frequency of patient-years (%). Total=511 yearsLetrozole19037Tamoxifen5611Capecitabine5511Exemestane438Fulvestrant316FEC245Paclitaxel235Docetaxel143Vinorelbine112Everolimus92

Conclusion: In this retrospective study of MBC patients, the expression of HR showed an individual positive impact of OS with a 50% reduction in hazards. In our cohort only the prognosis of HER2-/HR- patients were significantly worsened both in terms of PFS and OS compared to HER2-/HR+ subtype. In the analysis of HER2-/HR+ subtype, letrozole was the most durable therapy, used 37% of total treatment time. The most used chemotherapy was capecitabine, used in 11% of the treatment time.

Citation Format: Lindman H, Szilcz M, Freilich J, Carlqvist P, Vertuani S, Anell B, Holm B. Treatment patterns and outcomes of different subtypes of metastatic breast cancer patients in a Swedish real world setting with a focus on HER2-/HR+ subtype [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-16-10.