Inclusion Criteria:  Patients must be ≥ 18 years old and ≤ 75 years old Triple negative breast cancer (TNBC) patients (biopsy-proven) stage II-IV eligible >50%Programmed death-ligand 1 (PD-L1) positive Eligible for immunotherapy who are naïve to beginning any immunotherapy treatment May not be pregnant or breastfeeding Subjects must be willing to sign consent Adequate creatinine clearance per institutional guidelines and within 30 days Estimated life expectancy of greater than one year Patients must have one lesion with RECIST measurable disease (greater than 1 cm in diameter, measured from diagnostic breast MRI or staging CT)  Exclusion Criteria:  Inability to provide informed consent Weight over 350 lbs., due to the scanner bore size Lactating, known or suspected pregnancy. Women with child-bearing potential must a have a negative serum Human chorionic gonadotropin (β-hCG) pregnancy test within 48 hours or a negative urine β-hCG pregnancy test within 24 hours of each PET imaging study. Contraindication for MRI study (e.g. non-removable metal implants or certain tattoos) Unable to lie still on the imaging table for one (1) hour contraindication for gadolinium-based contrast agent, ProHance (gadoteridol) Have received immunotherapy in the neoadjuvant or adjuvant setting