Abstract PR13: Surgical excision of the primary tumor in osteosarcoma model results in enhanced metastatic growth by modulating the lung immune microenvironment
Authors: Kallis Michelle P. , Maloney Caroline , Edelman Morris , Soffer Samuel Z. , Symons Marc , Steinberg Bettie M. 
Published: August 2020

Abstract
Surgery has been shown to enhance metastasis in a number of cancers. To examine this in the context of osteosarcoma, we implanted syngeneic murine K7M2 cells into the tibia of BALB/c mice, which we had shown previously to result in immediate seeding of K7M2 cells into the lung. One week post-implantation, mice were assigned to either control or surgical groups and all mice were euthanized at week 4 post-implantation. Mice that underwent amputation of the primary tumor displayed an increase in the number of pulmonary surface nodules as compared to tumor-bearing control animals (17 vs. 9.5; p&lt;0.05), showing that excision of the primary tumor indeed enhances metastasis in this model. As we previously showed that K7M2 metastasis without surgical intervention is strongly inhibited by re-educating tumor-associated macrophages (TAMs) with gefitinib, we also examined the effect of gefitinib on surgery-accelerated metastasis. We found that perioperative gefitinib abrogated the effects of primary tumor removal on the development of pulmonary metastases (17 vs. 6; p&lt; 0.01), strongly suggesting that TAMs also mediate surgery-accelerated metastasis. To examine changes in the pulmonary immune milieu, we utilized the same model of surgery-accelerated metastasis. Lungs were homogenized and immune cell populations were analyzed using flow cytometric analysis at 48 hours and 3 weeks after surgery. We found that surgery caused a significant reduction in antitumor macrophages, identified by MHCII positivity (21.1% vs. 13.2%; p&lt;0.01), and a significant increase in protumor macrophages, identified by CD206 positivity (33.0% vs. 42.4%; p&lt;0.01), at 48 hours after surgical resection. There was no change in the proportion of CD4+ or CD8+ T cells at this time point. At 3 weeks post-surgery the proportion of macrophage populations became similar for both groups, but there was now a small but significant reduction in the CD4+ and CD8+ T cells in the surgical group (68.4% vs. 60.3%; p&lt;0.05 and 25.0% vs. 19.3%; p&lt;0.01). In conclusion, surgical removal of the primary tumor accelerated the growth of pulmonary metastases in a murine model of OS. Gefitinib was able to abrogate this effect, suggesting macrophages as key cellular mediators. Furthermore, surgery altered the macrophage phenotype within the lungs in the acute postoperative period toward a protumor state, subsequently reducing the CD4+ or CD8+ T-cell populations. Taken together these data suggest that surgery contributes to enhanced metastatic outgrowth by altering the immune microenvironment to an immunosuppressive and protumor state.
This abstract is also being presented as Poster B38.
Citation Format: Michelle P. Kallis, Caroline Maloney, Morris Edelman, Samuel Z. Soffer, Marc Symons, Bettie M. Steinberg. Surgical excision of the primary tumor in osteosarcoma model results in enhanced metastatic growth by modulating the lung immune microenvironment [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr PR13.