Rare cancers present a paradox. Individually, the number of people affected makes it difficult to attract funding for research, or even to build acceptably sizeable cohorts for randomized clinical trials. Yet these cancers account, collectively, for 25% of all cancer cases, and an even higher percentage of cancer-related deaths.

As methods of detection and knowledge of cancer improve, the increasing identification of molecular subsets of common cancers will lead to a larger number of cancers being grouped into the “rare” category.

“Some rare cancers are clear-cut independent disease entities of low frequency…whereas others are unusual subtypes of mainstream cancers,” the authors of a recent editorial wrote. “The latter is important because of the way we typically undertake research — such unusual subtypes are subsumed in large cohorts of common cancers, with no statistical power to discern their potential genetic uniqueness and very often they simply remain undetected, hidden amongst the common subtypes.”1

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That, the authors argued, puts rare cancer researchers and patients at a huge disadvantage.

“Genomic medicine, imperfect as it may be, is providing some patients with longer, better lives,” they noted. “And yet, [about] 1 in 4 patients with cancer will have these new therapeutics denied in the near future because of the way national grant agencies and research-focused charities are prioritising the administration of scientific resources.”

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The authors of another study noted that randomized clinical trials, which are considered the standard method of determining a drug’s efficacy, are not feasible for rare cancers because of limited potential participant availability.2

“To effectively address the deficiencies of the current clinical trial methodology, regulatory agencies need to continue to reassess current clinical trial protocols as applied to the study of rare cancer treatments,” they noted. “Perhaps new approaches that incorporate uncontrolled studies and/or observational evidences can be utilized.

“Conducting clinical research for rare cancers poses many challenges: lack of clinical expertise; drug developers have less incentive to study rare cancers since the potential market is small; the public sector tends to focus on funding those with the greatest need; rigorous study design requires large numbers of patients; recruitment goals are rarely feasible; selection of experimental treatments is often based on inadequate or minimal evidence; and limited tissue repositories are available.”