An Immunocompetent Murine Model of Metastatic Mammary Cancer Accessible to Bioluminescence Imaging

a and b, Sequential bioluminescent imaging in representative individual animals. Note that the increased intensity of the bioluminescent signals correlated with increased tumor size. a, The right axillary region (arrow) showed signal at 6 weeks while the right mandibular region (arrow) and left femoral region (arrow) bioluminesced 8 weeks post-inoculation in animal #2. b, Animal #3 showed signals in both the axillary (arrows) and left femoral regions (arrow) at 9 weeks post-inoculation. c-h, Histopathologies of the primary mammary carcinoma (c, ×200) and of metastases (d-h). The primary tumor arising at the inoculation site proved to be a moderately differentiated adenocarcinoma (animal #2). Within the same mouse, metastases developed in the mandibular lymph node (d, ×100), the axillary lymph node (e, ×100), and the femoral lymph node (f, ×100) — all of which were detected in imaging in the ventral plane. However, small metastatic foci found upon necropsy in the lungs of animal #2 (g, ×40) and the ovary from animal #3 (h, ×100) were not detected in ventral bioluminescence imaging. c-h, H&E stain.

a-f, Correlation of bioluminescent imaging and macroscopic and histological findings in representative mice. With animal #5 placed in the venter up position, the signals observed in regions corresponding to the primary tumor (*) and lymph nodes (a, black arrows indicate axillary, mandibular, iliac, and femoral lymph nodes) correlated to macroscopic abnormalities at necropsy findings (b, * and black arrows). Furthermore, focal signals (a, white arrows) appeared to emanate from prominent vessels observed at necropsy (b, white arrows) and may indicate tumor cells present in the lumens of distended lymphatic vessels (g, arrows, ×400) as seen with podoplanin immunohistochemistry. Dorsal imaging successfully detected macroscopic abnormalities in the kidneys and adrenals not apparent with ventral imaging of animal #5 (c); metastasis was histologically confirmed in femoral lymph nodes (h, ×400), lungs (i, ×40), kidney (j, ×40), and adrenals (k, ×200). In animals #1 and #4, luminescence was detected in areas corresponding to mandibular, axillary, and femoral lymph nodes (d and e); the large area of signal seen in animal #1 in panel f corresponded to liver metastasis (l, ×100). g, podoplanin immunohistochemistry; h-l, H&E stain.