Background: Tumor ablation is a minimally invasive technique commonly used to treat solid tumors in the liver, kidney, bone, and lung and is usually based on thermal and nonthermal approaches. Local and in-situ tumor ablation methods demonstrate enhanced anti-tumor immune responses resulting in the destruction of residual malignant cells in primary tumors and distant metastases. Nitric oxide (NO) is a colorless gas and a short-lived free radical. It is a ubiquitous, endogenously generated gas implicated in the homeostatic regulation of physiological processes. Preclinical studies evaluating the effect of high concentration exogenously administered NO demonstrated its anti-cancer properties and suggested that it may serve as a potent tumoricidal agent. We have previously shown that treating mouse colon carcinoma (CT26) tumor-bearing mice with ultra-high concentrations of nitric oxide (UNO101) upregulates innate and adaptive immune cells both locally and systemically. Beyond Cancer is currently conducting a first-in-human, first-in-class, Phase 1 safety, feasibility, and preliminary efficacy clinical study of UNO101 at multiple institutions in Israel. Methods: The study is a 2-part Phase 1 trial with a Dose Escalation and a Dose Expansion portion (NCT05351502). A conventional 3+3 dose escalation will evaluate three cohorts of UNO101 single dose: 25,000, 50,000 and 100,000 parts per million (PPM) delivered intratumorally over 5 minutes in subjects with an ECOG PS of 0–3, at least 3 months of life expectancy, with relapsed or refractory unresectable primary or metastatic cutaneous and subcutaneous measurable solid tumors being eligible for enrollment. Upon determination of the maximum tolerated dose or biological effective dose, whichever occurs first, the proposed recommended Phase 2 dose will be further evaluated in the Dose Expansion portion of the study. RECIST version 1.1 and iRECIST will be utilized to assess the rate of malignant tumor response after UNO administration and toxicity will be graded per NCI CTCAE version 5.0. Evaluation of response per itRECIST will also be explored. Up to thirty-eight enrolled subjects are anticipated. Cohort 1, 25,000 PPM have been completed without a reported DLT. Enrollment to Cohort 2, 50,000 PPM, began in January 2024. This study was approved by Israel Ministry of Health (IMOH) as well as the participating institution’s Ethics Board. Written informed consent was obtained for all enrolled subjects and a copy of the written consent is available for review. Clinical trial information: NCT05351502.