Summary The principal goal of this proposal is to demonstrate equivalence in efficacy of CO2- based percutaneous cryotherapy compared to commercial argon-based devices in order to improve the accessibility of a novel low-cost breast cancer treatment device for women in low-resource areas. Breast cancer is the leading cause of cancer death among women worldwide. Though more than 800,000 women are diagnosed each year in low-and-middle-income countries, standard treatment options are inaccessible and unaffordable in these low resource settings, and over half of these women will die within five years. Kubanda Cryotherapy offers a low-cost, non-resource-intensive breast cancer treatment that can be done in local clinics under local anesthetic and ultrasound guidance. Initial validation has been done on the current research prototype to demonstrate the effectiveness in cooling and necrosing cancer tissue in animal models including rats, swine and canines. This proposal aims to show that CO2-based percutaneous cryotherapy, although requiring a longer treatment period, is equally effective in necrosing cancerous masses compared to rapid freeze rate cryotherapy. To achieve this goal, we will perform cryotherapy using both rapid and slow freeze rate devices on twelve client-owned dogs with naturally developed mammary tumors. We will also quantitatively compare the cooling power of the two devices via calorimetry to obtain crucial understanding on key parameters and limitations related to procedure efficiency in order to continue further implementation of this technology. The main output of this project will be a robust and well- controlled cryotherapy device demonstrated to have equivalent efficacy to commercially available systems. Successful completion of this work will be an important step towards bridging the gap in breast cancer treatment in LMICs and offering women a chance at treatment. Upon completion of this proposal, we will apply for a Phase II award proposing to file IRB approval and begin clinical trials on the Kubanda cryotherapy device in order to bring low cost, affordable and effective breast cancer treatment to underserved communities worldwide.