NOS2 and neoplasm: In orthotopic TNBC models, noninvasive bioluminescent imaging, ultrasound-guided photoacoustic imaging, and histological analysis revealed that intravenous injection of RFP-tagged exosomes promoted primary tumor growth and axillary LN metastasis in which expression of CD206, a marker or alternatively activated type 2 (M2) macrophages, was significantly higher than expression of NOS2, a marker of classically activated type 1 (M1) macrophages.