  First, scientific classifications of cancer have as yet failed to yield a unified taxonomy. There is a diversity of classificatory schemes for cancer, and while some are hierarchical, others appear to be “cross-cutting,” or non-nested. Initially, researchers investigating cancer genomics seemed to think such issues might be resolved by molecular “subtyping”. However, genomic sequencing and its sequelae—transcriptomics, proteomics, epigenomics, etc.—have, if anything, complicated cancer classification. This literature thus raises a variety of questions about the nature of the disease and disease classification: Are there some classifications that are more useful, or better than others? What makes a classification a good one? What does it mean to track more or less “natural” distinctions in the context of disease? Is such talk of the “naturalness” of disease categories simply confused? The problem of cancer classification is complicated by the fact that cancer progression is a process with a complex natural history. Thus, cancer serves as a challenging case for disease classification, and also for demarcating disease from health, raising intriguing questions about the potential role(s) of precautionary values in cancer diagnosis.