Interstitial laser immunotherapy for treatment of metastatic mammary tumors in rats

Thermal therapy has been used for cancer treatment for more than a century. While thermal effect can be direct, immediate, and controllable, it is not sufficient to completely eradicate tumors, particularly when tumors have metastasized locally or to the distant sites. Metastases are the major cause of treatment failure and cancer deaths. Current available therapies, such as surgery, radiation, and chemotherapy, only have limited curative effects in patients with late-stage, metastatic cancers. Immunotherapy has been considered as the ultimate approach for cancer treatment since a systemic, anti-tumor, immunological response can be induced. Using the combination of photothermal therapy and immunotherapy, laser immunotherapy (LIT), a novel immunotherapy modality for late-stage cancer treatment, has been developed. LIT has shown great promise in pre-clinical studies and clinical breast cancer and melanoma pilot trials. However, the skin color and the depth of the tumor have been challenges for effective treatment with LIT. To induce a thermal destruction zone of appropriate size without causing thermal damage on the skin, we have developed interstitial laser immunotherapy (ILIT) using a cylindrical diffuser. To determine the effectiveness of ILIT, we treated the DMBA-4 metastatic tumors in rats. The thermal damage in tumor tissue was studied using TTC immersion and hematoxolin and eosin (H & E) staining. Also observed was the overall survival of the treated animals. Our results demonstrated that the ILIT could impact a much larger tumor area, and it significantly reduced the surface damage compared with the early version of non-invasive LIT. The survival data also indicate that ILIT has the potential to become an effective tool for the treatment of deeper, larger, and metastatic tumors, with reduced side effects.