Cancer affects all of humankind, but there are marked differences across local, national, and regional boundaries, particularly when considering specific tumour types rather than cancer as a whole. Epidemiological data on incidence of cancer and deaths caused by cancer vary enormously in coverage and quality between countries and regions worldwide, ranging from complete coverage by national cancer registries to population-based registries, or no available data at all on cancer occurrence. In the absence of data, inferences must be drawn from surrounding countries to provide the best estimate possible.

Among men, the five most common sites of cancer diagnosed in 2012 were lung (16.7% of the total), prostate (15%), colorectum (10%), stomach (85%), and liver (7.5%). Among women, the five most common incident sites of cancer were the breast (25.2% of the total), colorectum (9.2%), lung (8.9%), cervix (7.9%) and stomach (4.8%).

Among men, lung cancer had the highest incidence (34.2 per 100 000) and prostate cancer had the second highest incidence (31.1 per 1000 000). Among women, breast cancer had a substantially higher incidence (43.3 per 100 000) than any other cancer; the next highest incidence was colorectal cancer (14.3 per 100 000).

Cancer is a global problem. Of the roughly seven million cancer deaths that occur worldwide, approximately 70% of these are in low and middle-income countries. The majority of the 27 million new cancer cases and 17 million cancer deaths that will occur by 2020 will also occur in resource-limited nations. Further, the likelihood of death from a particular type of cancer differs drastically from country to country. A woman with breast cancer in a high-income country has, on average, a less than 25% chance of dying from her disease, while the same woman in a low-income country has close to 60% chance of death. Disparities in access to timely diagnosis, and high-quality treatment likely explain these extremely different odds in survival for the same disease.

Common misconceptions have held that cancer is a disease of the wealthy, while poorer nations struggle exclusively with communicable diseases. In reality, cancer is and has always been a real burden in low and middle-income countries. More people die of cancer than of HIV, TB, and malaria combined, and two thirds of these deaths are in the developing world. Further, as people live longer and communicable diseases are addressed, the burden of cancer in low and middle-income countries is rising. By 2030, cancer will be the leading cause of death in these settings causing over 10 million deaths.