CD40 Agonist, Flt3 Ligand, and Chemotherapy in HER2 Negative Breast Cancer

This trial tests a novel immune-activating combination therapy for advanced (stage III or IV) HER2-negative breast cancer — meaning it is either triple-negative or hormone receptor-positive but HER2-negative. The combination includes a CD40 agonist (to activate the immune system), Flt3 ligand, and chemotherapy. **You may be eligible if...** - You are 18 or older - You have unresectable Stage III or Stage IV HER2-negative breast cancer (triple-negative or hormone receptor-positive) - Your cancer has progressed during or after your last cancer therapy - You are in reasonably good health (ECOG 0–2) with a life expectancy of at least 12 weeks **You may NOT be eligible if...** - Your cancer is HER2-positive - You have certain serious medical conditions (serious infections, autoimmune disease, prior organ transplant) - You have had brain metastases that are untreated or unstable - You have received specific prior therapies that make you ineligible per the protocol Talk to your doctor to see if this trial is right for you.