Atavistic theory: cancer as a reversion to an ancient programme

The claim. Multicellularity was built on top of an older, highly conserved programme for single-cell survival and proliferation. Cancer is that programme de-repressed when the newer, more fragile layers of multicellular control fail; the tumour behaves like a colony of early metazoan cells ('Metazoa 1.0'). Because the toolkit is ancient and conserved, cancer's capabilities (unlimited division, fermentative metabolism, motility, resistance to hypoxia and toxins) are pre-assembled rather than assembled anew by random mutation, which explains why tumours converge on the same hallmarks so quickly. Mark Vincent's version (2012) frames cancer as the default life-history strategy of a cell under stress once the cooperative contract of multicellularity is broken.

Who and when. Davies and Lineweaver, Cancer tumors as Metazoa 1.0, 2011; Vincent, Cancer: a de-repression of a default survival program common to all cells?, 2012; Lineweaver, Davies and Vincent on therapeutic implications, 2014. Related lines: Aktipis and colleagues on cancer across the tree of life (2015), and the phylostratigraphic analyses of Trigos and colleagues (2017) and Bussey and colleagues (2017).

Evidence for. Cancer occurs in nearly every multicellular lineage, which implies an ancient shared vulnerability. Genes upregulated in tumours are enriched for those that arose in unicellular ancestors and genes downregulated are enriched for those that arose with multicellularity; the interactions between the two gene classes are disrupted (Trigos 2017). The hallmarks resemble the behaviours of free-living single cells. Bussey and colleagues found that ancestral gene regulatory networks are re-engaged in cancer.

Evidence against and limits. No coordinated ancestral programme has been shown to switch on as a unit; the gene-age correlations are consistent with other explanations, such as proliferation genes simply being old. Many cancer traits (immune checkpoint expression, specific drug efflux pumps) are recent, not ancient. The theory is largely a reframing of known biology rather than a source of new predictions, and critics regard it as a metaphor. It has produced no therapy and no validated biomarker.

Predictions that held or failed. Held: phylostratigraphic patterns in tumour gene expression. Unfulfilled or untested: the proposal that cancers can be attacked through the weaknesses of an ancestral programme (for instance intolerance of high oxygen or of environments the ancient toolkit never met) has not been tested in patients.

Therapies that came from it. None. Its authors suggest targeting the programme's weaknesses rather than its strengths and lean on the metabolic theory (fermentation as an ancestral trait). It sits alongside the ecological view of cancer as an evolutionary process and challenges the somatic mutation theory's assumption that each tumour builds its capabilities from scratch.

Status: contested. An influential framing with some support from gene-age analyses, not yet a theory with confirmed predictions or therapeutic consequences.