01.10 Establishment of Metastatic Breast Cancer to the Lung by Surgical Implantation

M. Oshi1, M. Okano1, A. L. Butash1, K. Takabe1  1Roswell Park Cancer Institute,Department Of Surgical Oncology,Buffalo, NY, USA

Introduction: Although targeted therapies in primary breast cancer have significantly improved the survival rate in the last two decades, the challenge to improve the survival rate in patients with metastatic breast cancer still remains. Pre-clinical models play an important role in developing treatment strategies, but proper breast cancer metastasis models have not been established due to the difficulty and complication of the procedure. We developed the “thoracotomy” method in order to establish a breast cancer lung metastasis model, which is simple and resembles human lung metastasis. 

Methods: All work was performed in female NSG or bulb/c mice of age 8-12 weeks. PDX of lung metastasis model was made from patient-derived breast tumors. PDX breast tumors that had been passaged 3 times in mammary fat pads or lung metastasis tumor generated using 4T1 cell line were used. Tumors were diced to ~1 mm3 pieces using a sharp blade. 

Results: The right middle lobe was selected as an implantation site in order to allow the tumor to invade the lung and not the chest wall. In the “thoracotomy” method, the chest wall incision was made and tumor fragments were implanted using forceps and 8-0 nylon surgical suture. Another approach was to directly inject the minced tumor tissue 1mm below the lateral pleural surface of the middle lobe using a 23G needle. The incision was closed with a 6-0 surgical suture. An intrathoracic puncture was made with a 27G needle to withdraw the remaining air from the chest cavity. After the air had been withdrawn, a completely inflated lung could be seen through the thin chest wall. In the “non-thoracotomy” method, the minced tissue was injected into the mice lung through the chest wall with a 23G needle. One hour post-surgical survival rate was only 30% after “thoracotomy” method (non-fixing suture 9/30, fixing suture 8/30) due to open pneumothorax resulting from excessive wound tension and intercostal muscle cut through. All mice after “non-thoracotomy” method survived, but implantation in the chest wall was observed in 67% (4/6) of cases and the method achieved only 50% (3/6) of the accurate transplantation into the middle lung when performed preliminarily using the cell line.  To increase the survival rate with the “thoracotomy” method, we limited the incision size <10 mm and compared the outcome with the original incision group. Limited incision “thoracotomy” could significantly increase one hour post-surgical survival to 97% (29/30) (<10 mm vs. ≥10 mm: t test P = 0.003). 

Conclusion: By simple modifications of surgical techniques, we are able to establish an orthotopic lung metastasis mice model with almost zero operative mortality. Our orthotopic thoracotomy model has the potential to be a powerful tool for preclinical studies of breast cancer patients with lung metastases.