The US Has Higher Incidence, Survival of Rare Cancers Compared With Europe

The incidence of rare cancers is higher in the United States than in Europe, but so is the survival rate, according to a study published in Cancer Medicine.

Diagnosis of rare cancers is often delayed, research can be difficult, and clinical management is complex, which results in inferior outcomes in rare cancers compared with common cancers. The authors used a revised definition of cancer entities from the World Health Organization and a common methodology to compare incidence and survival of rare cancers in the United States and Europe.

“These comparisons have the potential to highlight important differences and improve our understanding of [rare cancers] in both locations,” the authors explained.

They used incidence and survival data from 18 Surveillance, Epidemiology, and End Results registries and 94 European registries. The time period studied was 2000 to 2007, because this was the most recent period that had available European data.

While the crude annual incidence rate for rare cancers was lower in the United States, the European population was older. Age-specific incidence rates were lower in Europe.

The authors excluded 3 cancers because they were not rare in both Europe and the United States. They found that thyroid carcinoma and diffuse B-cell lymphoma were classified as rare in Europe based on incidence but were common in the United States, and breast invasive lobular carcinoma was common in Europe but rare in the United States.

A total of 196 rare cancers were included; however, only 43 had significantly different incidence rates among the 2 populations. Of these 43 rare cancers, 34 had higher incidence rates in the United States. Age-adjusted incidence for all rare cancers combined was 17 percentage points higher in the United States than in Europe. The 5-year net survival for all rare cancers was significantly higher in the United States compared with Europe (54% vs 48%).

The authors speculated that risk factors, overdiagnosis, differences in the ability to diagnose rare cancers, and different registration practices and use of classification codes among the 2 populations may explain why the United States has higher incidence and survival rates for rare cancers. For instance, obesity is more prevalent in the United States and it can be a risk factor for a number of cancers.

The authors also noted that the different health system organization among the 2 regions may also result in differences. The private health system in the United States may lead to more intensive investigations, thus producing a higher incidence rate and higher incidence of early-stage cases. When cancers are caught at an earlier stage, the outcomes are more favorable.

“Our findings suggest opportunities for further research to understand the burden of [rare cancers] and to spur greater international collaboration on the study of [rare cancers], with the goal of greater awareness, knowledge and therefore providing inputs in their prevention, diagnosis and treatment,” the authors concluded.

Reference

Botta L, Gatta G, Trama A, et al. Incidence and survival of rare cancers in the US and Europe. Cancer Med. Published online May 21, 2020. doi:10.1002/cam4.3137