BACKGROUND: The invasion of Ukraine by Russia in February 2022 has resulted in destruction of healthcare infrastructure and triggered the largest wave of internally displaced populations and refugees since World War Two. Conflicts in transitioned countries such as Ukraine create new non-communicable disease (NCD) challenges, especially for cancer care for refugees and humanitarian assistance in host countries. In the early days, rapid attempts were made to model possible impacts. METHODS: By evaluating open source intelligence used in the first three months of the conflict through snowball search methods, we aimed to address: (i) burden of cancer in Ukrainian population, specifically considering translating to the refugees population, and its cancer care capacity; ii) baseline capacity/strengths of cancer systems in initial host countries. Moreover, using a baseline scenario based on crude cancer incidence in Ukraine, and considering data from UNHCR, we estimated how cancer cases would be distributed across host countries. Finally, a surveillance assessment instrument was created, intersecting health system's capacity and influx of internally displaced populations and refugees. FINDINGS AND CONCLUSIONS: The total new cancer patients per month in pre-conflict Ukraine was estimated as 13,106, of which < 1 % are paediatric cases. The estimated cancer cases in the refugee population (combining prevalent and incident), assuming 7.5 million refugees by July 2022 and a female:male ratio of 9:1, was 33,121 individuals (Poland: 19284; Hungary: 3484; Moldova: 2651; Slovakia: 2421; Romania: 5281). According to our assessments, Poland is the only neighbouring country classified as green/yellow for cancer capacity, i.e. sufficient ablility to absorb additional burden into national health system; Slovakia we graded as yellow, Hungary and Romania as yellow/red and Moldova as red.