Cancer as Clonal Evolution: Drivers, Passengers and Selection in a Tissue
A tumour is a cell population under selection inside a body, so population genetics applies to it directly. This stop separates driver from passenger mutations and reads a tumour's history out of its mutation data.
What a learner can do afterwards
- Argue from recurrence and mutation frequency whether a gene is a plausible driver
- Explain what subclonal structure in a sequenced tumour says about the order of events
- Apply selection and drift arguments to a growing population of somatic cells
1 · Read
You read a tumour as a cell population under selection inside a body. Mutations that speed growth are favored, their carrier cells expand into clones, and fresh mutations arise within those clones. Sequencing a tumour reads out an evolutionary tree written in somatic mutations.
You separate drivers from passengers with recurrence, not single tumour frequency. A gene hit repeatedly across independent patients, at the same functional sites, has almost certainly been selected. A gene mutated once at a random spot is likely a passenger carried along by a fast dividing clone.
You compare two mutations in one patient. One sits in every tumour cell, so it came before the last clonal expansion. The other sits in a fraction of cells, so it came later within one branch. Their nesting reconstructs the order from founding lesion to latest aggressive subclone.
You apply selection and drift arguments to somatic cells directly. A driver is a beneficial allele sweeping its clone upward, while passengers are neutral alleles hitchhiking beside it. Therapy is fresh selection, so resistance often expands a rare subclone that already existed.
You call drivers by recurrence across tumours, you date events by subclonal nesting, and you expect selection to act on every clone.
More to read
10.4 Cancer and the Cell Cycle
The cell cycle runs on checkpoints that halt division until DNA is intact and conditions are right. Cancer begins when mutations disable these brakes, letting cells divide without permission. Each division risks fresh mutations, and the population of abnormal cells grows. This is evolution on fast forward inside one tissue. Mutations that speed growth are favored, their carrier cells expand into clones, and new mutations arise within those clones. Sequencing a tumour therefore reads out an evolutionary tree written in somatic mutations.
16.7 Cancer and Gene Regulation
Tumours misregulate the same gene expression programs that healthy cells control tightly. Growth signals stay on, repair genes fall silent, and the mutation rate itself often rises as repair fails. Genes hit repeatedly across independent patients stand out against this noisy background. Recurrence is the key driver test. A gene mutated in many unrelated tumours, at the same functional sites, has almost certainly been selected. A gene mutated once at a random spot is more likely a passenger carried along by a fast dividing clone. Frequency within one tumour means little, recurrence across tumours means a lot.
19.1 Population Evolution
Populations evolve as allele frequencies shift under selection and drift, and a growing tumour is a population of somatic cells. A driver mutation is simply a beneficial allele in this microcosm, sweeping its clone to high frequency. Passengers are neutral alleles hitchhiking beside it. Subclonal structure dates the events. Mutations present in every tumour cell occurred before the last clonal expansion, while mutations found in only a fraction came later within one branch. Reading these nested frequencies reconstructs the order in which drivers struck, from the founding lesion to the latest aggressive subclone.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.