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GP2+GM-CSF vaccine versus GM-CSF alone administered in the adjuvant setting to high-risk breast cancer patients


GP2 is a HER2 derived, HLA-A2+-restricted immunogenic peptide designed to stimulate CD8+T cells to recognize tumor cells with any level of HER2 expression ( IHC 1-3+ ). Accrual to a prospective, randomized, multi-center, phase II trial of the GP2 vaccine for prevention of breast cancer recurrence has completed.

The planned primary analysis of disease-free survival ( DFS ) has been presented.

HLA-A2+ node positive or high-risk node negative breast cancer patients with any level of HER2 expression rendered disease-free by standard of care therapy ( to include Trastuzumab [ Herceptin ] where appropriate ) were randomized to receive GP2+GM-CSF ( VG ) or GM-CSF ( CG ) alone.
Patients received 6 monthly inoculations ( primary vaccine series = PVS ) followed by 4 boosters administered every 6 months.

The Kaplan Meier method was used for statistical analysis. The intention-to-treat ( ITT ) population is defined as the entire randomly assigned population. The per-treatment ( PT ) group excluded patients who recurred during the primary vaccine series or developed a second malignancy. A pre-specified subgroup analysis was performed based on HER2 expression level. HER2 overexpression ( OE ) is defined as IHC 3+or FISH greater than 2.2.

With 89 GP2+GM-CSF and 91 GM-CSF patients enrolled and vaccinated, there are no differences between groups with respect to age, node positivity, tumor size, grade, ER/PR status, and HER2 expression ( p greater than 0.05 ).

The vaccine has been well tolerated with toxicities comparable between the GP2+GM-CSF and GM-CSF. Only one grade 3 local and systemic toxicity reaction has been reported in the GP2+GM-CSF.

At 34 ( 1-60 ) month median follow-up, disease-free survival was compared in the ITT ( 85% GP2+GM-CSF vs 81% GM-CSF, p = 0.57 ) and PT ( 94% vs 85%, p = 0.17 ) populations.

In patients with HER2 overexpression ( 51 GP2+GM-CSF and 50 GM-CSF ) disease-free survival was 94% vs 89%, p = 0.86 ( ITT ) and 100% vs 89% p = 0.08 ( PT ).

In conclusion, GP2+GM-CSF is a novel vaccine that is safe and well tolerated. This phase II trial has demonstrated potentially greater benefit in patients with HER2 overexpression tumors, in whom there have been no recurrences in the PT group. This may be due to synergism with Trastuzumab therapy, thus justifying a phase III trial evaluating GP2 administered in the adjuvant setting to a HER2 overexpression population. ( Xagena )

Source: Breast Cancer Symposium, 2014

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