Inherited cancer susceptibility
Everyone in the population is at risk of developing cancer
at some point in their lives. Not everyone who has cancer
will necessarily have inherited a faulty copy of a
In the general population (where there is not an inherited
faulty susceptibility gene that causes a predisposition to
cancer), cancer develops as a result of a cascade of genetic
changes to a single cell and its descendants leading to
uncontrolled growth in a subset of cells in the body.
Because the genetic mistakes are accumulated over time, the
risk of developing cancer increases with age. In an
individual who has a faulty cancer susceptibility gene
present, the faulty gene is usually present in every cell in
the individual (including the embryo).
This means that fewer genetic mistakes are needed to
accumulate in an individual cell of that person for cancer
to develop, since the cell already contains one mistake.
Because less time is needed to accumulate the mistakes,
cancer often develops earlier in people who inherit a faulty
susceptibility gene than in people with the sporadic cancer.
For example, women that have an inherited fault in the gene
that causes breast cancer are more likely to develop it in
their late thirties and forties, whereas women that develop
the cancer sporadically are more likely to get it in their
sixties and seventies.
These inherited cancer susceptibility
conditions are responsible for only a small proportion of
cancers in the population.
About 5% of individuals with common cancers have an
inherited cancer susceptibility condition. The risk of
developing cancer that is associated with a susceptibility
gene condition can vary depending on the specific condition.
Some genetic faults can cause a very high susceptibility to
specific cancers, such that almost all people who have the
faulty gene will develop the condition. These conditions are
called highly penetrant conditions. For other conditions,
having an inherited copy of the faulty susceptibility gene
only results in the cancer developing in a proportion of
individuals that carry the susceptibility gene.
conditions will be referred to as lower penetrance
High and Lower penetrance conditions