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.
2 · Watch
Take 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.