Investigators Initiate Post-Trastuzumab Trial of GLSI-100 in Patients With Invasive Breast Cancer

Investigators hope to duplicate promising phase 2b trial results with an experimental peptide vaccine in a population of nearly 500 patients with human epidermal growth factor receptor 2 breast cancer.

Patients who have progressed on trastuzumab, including trastuzumab biosimilars, will be enrolled in a phase 3 trial of a promising immunotherapy for the treatment of breast cancer recurrence, according to an abstract presented at the San Antonio Breast Cancer Symposium 2021.

The trial will evaluate the safety and efficacy of human epidermal growth factor receptor 2 (HER2)/neu peptide GLSI-100 in patients with residual disease or high-risk pathologic complete response (pCR) after neo-adjuvant and postoperative adjuvant anti-HER2 therapy.

GLSI-100 incorporates granulocyte-macrophage colony-stimulating factor and sargramostim, which contribute to the development of white blood cells and cells that become platelets; and GP2, which is a 9 amino acid transmembrane peptide of the HER2/neu protein. This combination is believed to stimulate an immune response targeting HER2/neu–expressing cancers.

In a randomized, placebo-controlled multicenter phase 2b study led by The University of Texas MD Anderson Cancer Center, no recurrences were observed after a median 5 years of follow-up if patients received the full 6 primary injections over the first 6 months of treatment.

“Furthermore, the immunotherapy elicited a potent immune response [as] measured by local skin tests and immunological assays,” authors of the abstract stated.

To date, 138 patients have been treated with GLSI-100 in 4 clinical trials, and investigators reported the therapy was well-tolerated with no serious adverse events related to the treatment.

“This phase 3 trial aims to reproduce the phase 2b trial and will explore the use of GLSI-100 as adjuvant therapy to increase invasive disease-free survival in HER2/neu–positive and [HLA-A*02–allele group] patients, postsurgery and following the first year of treatment with any trastuzumab-based therapy,” authors wrote.

Investigators will enroll 498 patients with residual disease or high-risk pCR (stage III) who are HER2/neu–positive and have the HLA-A*02–allele, which is common to individuals of European ancestry. Following initial trastuzumab therapy, patients will receive the 6 primary injections over 6 months, then 5 booster shots over 2.5 years, for a total of 11 injections. The trial duration will be 3 years with an additional year of follow-up.

End points are increased invasive disease–free survival, safety, and immunologic response to treatment.


Patel SS, McWilliams DB, Fischette CT, et al. A randomized, multicenter, placebo-controlled, phase III study to evaluate the efficacy and safety of HER2/neu peptide GLSI-100 (GP2 + GM-CSF) in patients with residual disease or high-risk PCR after both neo-adjuvant and postoperative adjuvant anti-HER2 therapy. Presented at SABCS 2021; December 7-10, 2021. Abstract: OT-18-07