Assessment of single-institution HER2 testing patterns, rate of HER2+ disease, and utilization of trastuzumab in early breast cancer.

Abstract

124 Background: Improved outcomes with HER2-directed therapies highlight the importance of standardized testing for HER2 positivity. This study aimed to assess HER2 testing practices, rate of HER2+ disease, and trastuzumab use in early breast cancer (EBC) at the Huntsman Cancer Institute (HCI) a National Cancer Institute-Designated Center and member of the National Comprehensive Cancer Network. Methods: Included patients’ records from the HCI electronic data warehouse (EDW) and the HCI tumor registry were female, age ≥ 18 years, ≥ 2 visits in the EDW and a stage I to IIIa EBC diagnosis from 2005 to 2012. HER2 testing patterns were identified through chart review of pathology and clinical notes in the EDW. HER2+ was defined as either FISH+ or IHC3+. Patient characteristics, HER2+ rate, and trastuzumab use were evaluated descriptively. Discordance rate associated with reflex testing (IHC 2+ retested by FISH) was also evaluated. Results: A total of 1,459 women were included with stage I (49%, n=720), IIa (26%, n=374), IIb (14%, n=197), and IIIa (12%, n=168) EBC. Mean age was 57 years. HER2+ disease was identified in 243 (17%) tumors. Of HER2+ tumors, 104 (43%) were ER+/PR+, 33 (14%) ER+/PR-, 1 (<1%) ER-/PR+, 79 (32%) ER-/PR-, and 26 (11%) unknown. Tumors were first tested for HER2 using: 1,192 (82%) IHC, 36 (3%) FISH, 227 (15%) unknown and 4 (<1%) other tests. First IHC results were scored 0 (23%), 1+ (33%), 2+ (26%), 3+ (17%), and unknown (<1%). Reflex testing within one month was performed in 301/308 (98%) of IHC 2+ tumors. The discordance rate of IHC/FISH was 10%. Trastuzumab was prescribed for 184/243 (76%) women whose tumors were considered HER2+ based on final interpretation and in 1 HER2 equivocal tumor. Documented reasons for lack of trastuzumab use in HER2+ patients (n=59) included low risk of recurrence based on stage or other treatments (n=18), loss to follow-up (n=13), unknown (n=11), not clinically appropriate due to age or comorbidity (n=10), and patient declined (n=7). Conclusions: This is one of few cancer registries assessing the rate of HER2+ disease in EBC. Reflex testing identified additional HER2+ tumors. The HER2+ rate was within range of previously published studies.