Table 2 An initial classification scheme

1

D1Δ1

H1R1

Like a desert, these tumours have few resources and little diversity. With low turnover, they are evolutionarily inert.

2

D1Δ1

H1R2

Much like normal tissue, these tumours have sufficient resources but evolve very slowly.

3

D1Δ1

H2R1

These tumours may have the best prognosis, with an immune response that probably helps to control the tumour, restricted resources and little capacity to evolve.

4

D1Δ1

H2R2

These tumours have ample resources but have also stimulated an antitumour immune response. However, they are otherwise evolutionarily inert.

5

D1Δ2

H1R1

These tumours are genetically homogeneous but are changing over time, perhaps through population bottlenecks or selective sweeps that re-homogenize the tumour.

6

D1Δ2

H1R2

These tumours are changing over time, potentially through homogenizing selective sweeps of new clones. While they may grow rapidly, with ample resources, their genetic homogeneity may make them vulnerable to therapy.

7

D1Δ2

H2R1

Predation by the immune system in these tumours may reduce genetic heterogeneity through selection against neo-antigens.

8

D1Δ2

H2R2

Natural selection may be driving the changes in these tumours and homogenizing them.

9

D2Δ1

H1R1

These tumours may be the result of the slow accumulation of clones over a long period of time or from exposure to mutagens.

10

D2Δ1

H1R2

Like a garden, these tumours support a variety of clones, are well fed and are protected from hazards such as predation, but they change little over time.

11

D2Δ1

H2R1

Accumulation of many mutations may have led to an immune response in these tumours, but they appear to be otherwise restricted in their growth and evolution.

12

D2Δ1

H2R2

These genetically diverse tumours are changing only slowly, perhaps due to a low mutation rate or relatively weak selective pressures.

13

D2Δ2

H1R1

These tumours are evolving rapidly, generating and maintaining new clones at a high rate. They are probably under selective pressure for the ability to survive and proliferate with scarce resources or otherwise escape these resource constraints.

14

D2Δ2

H1R2

With potentially the worst prognosis, these genetically diverse tumours are evolving rapidly and have plenty of resources. They should have the highest capacity to evolve in response to interventions or other changes in their environment.

15

D2Δ2

H2R1

These rapidly evolving and diverse tumours are under the dual selective pressures of resource limitations and immune predation.

16

D2Δ2

H2R2

Like a rainforest, these genetically diverse tumours are changing rapidly, with a constant churn of new clones evolving and others going extinct. Resources are abundant, although they are probably being consumed rapidly, and predation from the immune system is extensive.