INTRODUCTION: GK-1 is a safe and effective molecule with high antimetastatic activity against murine breast and skin cancer. GK-1 treatment enhances cytotoxic response of CD8 MATERIAL AND METHODS: BALB/c female mice were injected orthotopically with 1000 4T1 cells. When palpable primary tumors of about 1 mm RESULTS: Subcutaneous or intravenous administration of GK-1 significantly increased the lifespan of mice and significantly reduced the primary tumor weight and volume and the number of lungs macrometastases. GK-1 reduced the expression of PD-1 in tumor-infiltrating lymphocytes in mice regardless of the route of immunization used, which is especially encouraging. No evidence of damage to kidney or heart tissues was detected in the tumor-free mice. CONCLUSIONS: This study supports that subcutaneous GK-1 administered, has an efficacy non-inferior to intravenous administration, well-tolerated with a similar safety profile and therefore offers a less invasive valid treatment alternative.