Background

Patients with inflammatory breast cancer (IBC) have a poor prognosis, primarily due to distant dissemination. Additionally, IBC patients have an increased rate of HER2 overexpression when compared to patients with non-inflammatory breast cancer. The forms the rationale for HER2 directed tumor vaccine therapy in these patients. The purpose of this study was to examine overall survival in IBC patients receiving HER2 directed tumor vaccine therapy when compared with matched control patients from the SEER Registry.

Methods

Patients with diagnosis of Stage III or IV HER2 positive IBC having completed standard initial therapy and without evidence of disease received HER2 vaccinations after being enrolled on 5 prospective clinical trials. Overall survival data were pooled and analyzed. A control group of matched IBC patients were identified by querying the SEER database from 1997-2011. The control group was identified as any individual in the database with a code for IBC. A secondary analysis comparing survival in HER2 positive IBC vs HER2 negative IBC patients was performed by querying the SEER database from 2010 onwards, the time point when the HER2 status was coded in the database. Propensity score adjustment were made to the control group to account for any imbalances between groups in measured covariates such as stage, race, age, sex, and era of enrollment and the time interval from diagnosis to enrollment on vaccine trial (median ∼2 years).

Results

A total of 37 IBC patients received HER2 directed vaccine therapy and 676 patients were identified for the SEER control group; Stage at enrollment: stage IIIB: 30 patients in the vaccine group and 639 patients in the control group; stage IIIC: 1 patient in the vaccine group and 15 patients in the control group; stage IV 6 patients in the vaccine group and 22 in the control group. The median survival of the overall population was 112 months for the vaccine group and 47 months for the control group (p=0.04). After using propensity scores to adjust the control for imbalances in measured covariates, the median survival for the overall population was 112 months for the vaccine group and 37 months for the control group (p=0.03). There was no difference in survival between HER2 positive and HER2 negative IBC patients in the control group (p=0.6).

Conclusion

These results demonstrate promising overall survival in HER2 positive IBC patients receiving HER2 directed vaccine therapy after initial therapy. Propensity matching was performed to adjust for imbalances in measured covariates and resulted in a modest decrease in survival of the control group after adjustment, suggesting that the vaccine trial group had relatively unfavorable pre-treatment characteristics. Despite these unfavorable characteristics, patients receiving vaccine had a median survival of 112 months. These results must be further confirmed in a prospective randomized trial.

Citation Format: Rengan R, Baker K, Salazar L, Childs J, Higgins D, Redman M, Reichow J, Disis ML. Overall survival in inflammatory breast cancer patients receiving Her-2 Neu directed tumor vaccine therapy: Matched comparison with SEER registry patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-11-05.