Abstract
In preclinical studies, accurate monitoring of tumor dynamics is crucial for understanding cancer biology and evaluating therapeutic interventions. Traditional methods like caliper measurements and bioluminescence imaging (BLI) have limitations, prompting the need for improved imaging techniques. This study introduces a fast-scan high-frequency ultrasound (HFUS) protocol for the longitudinal assessment of syngeneic breast tumor grafts in mice, comparing its performance with caliper, BLI measurements and with histological analysis. The E0771 mammary gland tumor cell line, engineered to express luciferase, was orthotopically grafted into immunocompetent C57BL/6 mice. Tumor growth was monitored longitudinally at multiple timepoints using caliper measurement, HFUS, and BLI, with the latter two modalities assessed against histopathological standards post-euthanasia. The HFUS protocol was designed for rapid, anesthesia-free scanning, focusing on volume estimation, echogenicity, and necrosis visualization. All mice developed tumors, only 20.6% were palpable at day 4. HFUS detected tumors as small as 2.2 mm in average diameter from day 4 post-implantation, with an average scanning duration of 47 s per mouse. It provided a more accurate volume assessment than caliper, with a lower average bias relative to reference tumor volume. HFUS also revealed tumor necrosis, correlating strongly with BLI in terms of tumor volume and cellularity. Notable discrepancies between HFUS and BLI growth rates were attributed to immune cell infiltration. The fast HFUS protocol enables precise and efficient tumor assessment in preclinical studies, offering significant advantages over traditional methods in terms of speed, accuracy, and animal welfare, aligning with the 3R principle in animal research.