Abstract P3-07-21: Breast cancer subtype and survival in a population-based cohort of patients from California
Authors: Clark Christina A , Gomez Scarlett Lin , Tao Li , Moy Lisa , Yang Juan , Wang Lisa , Beattie Mary S , Eng-Wong Jennifer , Brammer Melissa , Chu Laura 
Published: May 2015

Background: Breast Cancer (BC) is a heterogeneous disease comprising distinct subtypes defined at present by tumor molecular markers. Over the past decades, more effective treatments targeted to specific markers have been developed and tested in clinical trials. While clinical trials have demonstrated the impact of these targeted treatments on recurrence and mortality rates, little is known about survival patterns associated with specific subtypes in the general population. We examined overall survival outcomes according to tumor subtype and stage in a diverse, population-based cohort of BC patients (pts) in California.

Methods: Through the California (CA) Cancer Registry, we identified all female CA residents diagnosed with primary invasive BC between 1/1/2005 and 12/31/2011. We classified these cancers as early breast cancer (EBC, stages I-III) vs. de novo metastatic (MBC, stage IV). We further grouped these cancers into 4 subtypes based on HER2 and hormone receptor (HR) status. For a subset of women with available survival data, we calculated the proportion surviving at 3 years (yrs), and median overall survival using the Kaplan-Meier method.

Results: 118,817 EBC pts (61.4% HR+/HER2-, 9.9% HR+/HER2+, 13.3% unclassified, 4.9% HR-/HER2+, and 10.6% triple-negative (TN)) and 6,268 MBC pts (43.7% HR+/HER2-, 13.0% HR+/HER2+, 23.3% unclassified, 8.9% HR-/HER2+, and 10.7% TN) were identified. Table 1 presents survival time in EBC vs. MBC, and for each of the receptor subtypes of BC. For EBC, 3-yr survival rate was highest (95.1%) for HR+/HER2- pts and shortest (84.3%) for TN. For the HER2- and HER2+ overall groups (regardless of HR status), 3-yr survival was similar (93.3% vs. 92.5%, respectively). The longest survival for de novo MBC was observed for the HR+/HER2+ subtype (median OS: 45.3 months (mos)), compared to 38.7 mos for the HR+/HER2- subtype, 23.1 mos for the HR-/HER2+ subtype and 12.7 mos for the TN subtype. For the overall HER2+ and HER2- subtypes, HER2+ MBC had slightly better survival (3-yr rate: 47.6% and median OS: 33.6 mos) than HER2- MBC pts (3-yr rate: 44.8% and median OS: 30.9 mos).

Conclusions: This study demonstrates the relevance of subtype on the OS of BC pts in a large population of CA women. Although HER2+ status is a negative prognostic factor, survival was similar between HER2+ and HER2- pts, likely due to available treatments targeting HER2. TNBC pts had the shortest survival, especially when they presented with metastatic disease. There remains an urgent unmet need for more effective treatments for TNBC.

Table 1. Survival by stage (EBC vs de novo MBC) and BC subtypeEBCde novo MBCSubtypeN3-yr Survival (95% CI)N3-yr Survival (95% CI)Median OS (95% CI) (months)HR+/HER2-3811895.1 (94.8-95.3)135152.5 (49.8-55.1)38.7 (35.9-41.3)HR+/HER2+692094.6 (94.1-95.2)45055.1 (50.4-59.6)45.3 (36.5-50.5)Unclassified1081391.2 (90.6-91.7)89426.0 (23.1-28.9)11.9 (9.7-13.8)HR-/HER2+358988.4 (87.3-89.4)33337.5 (32.3-42.7)23.1 (19.2-27.4)TN708384.3 (83.4-85.1)35717.7 (13.9-21.9)12.7 (11.2-14.1)HER2-neg*4555093.3 (93.1-93.6)174544.8 (42.4-47.1)30.9 (28.6-33.6)HER2-pos*1063592.5 (92.0-93.0)79747.6 (44.0-51.0)33.6 (30.7-37.1)* Pts with available HER2 data, but missing HR data were included

Citation Format: Christina A Clark, Scarlett Lin Gomez, Li Tao, Lisa Moy, Juan Yang, Lisa Wang, Mary S Beattie, Jennifer Eng-Wong, Melissa Brammer, Laura Chu. Breast cancer subtype and survival in a population-based cohort of patients from California [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-07-21.