Cancer is often talked about in big and common categories like breast, lung, prostate and even brain cancer. What’s less understood is that a large percent of cancer patients are diagnosed with cancers most people have never heard of. These cancers are labeled “rare,” and that label carries real consequences for research, treatment, and survival.
Even though there is no single global rule, most health agencies follow similar benchmarks. In the United States, the National Cancer Institute generally considers a cancer rare if it affects fewer than 15 people per 100,000 annually.
The other criteria is if it results in fewer than about 40,000 new cases annually. In Europe, the benchmark is even lower. The cancer has to affect fewer than six persons per 100,000 people per year for it to be considered rare. A cancer may also be considered rare if:
That’s how conditions like malignant peritoneal mesothelioma, a cancer that forms in the lining of the abdomen found its way into the rare category.
Here’s the part that surprises a lot of people. While each rare cancer affects relatively few people, rare cancers combined account for about one in four new cancer diagnoses. In addition, they’re also responsible for roughly 25% of cancer-related deaths each year. They are considered serious issues because of their high mortality rate even with fewer diagnoses.
Once a cancer is classified as rare, it often falls into a funding blind spot. Research dollars tend to go towards large patient populations. This is because studies are easier to run, and potential treatments have bigger markets. As a result, rare cancers research suffers from:
For patients, that can mean months spent searching for answers, second opinions, or specialists who know the disease.
To address these issues, governments have stepped in with targeted programs. In the U.S., the Orphan Drug Act offers incentives like tax credits and market exclusivity. This is done to encourage drug companies to develop treatments for rare diseases.
International efforts, such as the International Rare Cancers Initiative, focus on pooling patients across borders. The goal is to ensure clinical trials can actually move forward. Without these policies, many rare cancers would likely be ignored altogether.
Calling a cancer rare is meant to describe numbers, but in practice, that label influences funding, research attention, and patient outcomes.
As rare cancers continue to make up a growing share of diagnoses, how they’re classified, and supported matters more than ever. For policymakers, researchers, and patients alike, these diseases prove that small numbers don’t necessarily mean small stakes.
