Ethnopharmacological disease classification and bioprospecting: the diversity of plant drugs used to treat cancer

Cancer is a highly-diverse disease and as the second-leading cause of death worldwide is a focus of drug discovery research. Natural products have been shown to be a useful source of novel molecules for the treatment of cancer. It is likely there are many plants with undiscovered molecules of therapeutic value, however identifying new leads from among the vast diversity of plants is very challenging. Traditional knowledge might inform bioprospecting by predicting lineages of plants rich in therapeutically useful molecules. Here, we characterise the phylogenetic diversity of plants used traditionally to manage cancer. We demonstrate the independent and repeated targeting of specific lineages of plants by different peoples in different parts of the world. That the same lineages are used to treat different cancers is suggestive of independent discovery of therapeutic value. However, the lineages we report here as rich in plants used traditionally to treat cancer coincide with those for other ethnobotanical applications, and contain few plants with proven anti-cancer activity. It is likely that the traditional knowledge recorded and explored here is shaped by selection of plants conferring milder effects for treating wider symptoms, such as tiredness or nausea, rather than for halting tumour growth. Accurate prediction of useful plant lineages for cancer management requires more nuanced information than is commonly provided in ethnobotanical records.