hereditary vs sporadic cancer
/ huh-RED-it-air-ee versus spuh-RAD-ik /
Imagine a long combination lock that must be fully cracked for a vault to open. Most people start with all the dials scrambled and must, through bad luck over a lifetime, happen to land each one in the wrong position. But a few people are born with one dial already set wrong — they begin life one step closer to the vault opening. That inherited head start is the difference between hereditary and sporadic cancer.
More precisely, cancer comes from an accumulation of DNA changes in a cell (the multi-hit model). In sporadic cancer — the large majority of cases — all of those changes are acquired during a person's life, in their body cells, from causes like aging, carcinogens, or simple random copying errors. None of these mutations were inherited, and they are not passed to children. In hereditary cancer, a person inherits one cancer-predisposing mutation (often in a tumor suppressor gene like BRCA1 or RB1) in every cell of their body from a parent, so each cell already carries one of the needed 'hits' from birth.
The distinction matters for risk and for families. People with a hereditary predisposition tend to develop cancer earlier and may have several affected relatives, which guides genetic counseling, earlier screening, and sometimes preventive measures. But two crucial points fight common misconceptions: first, inheriting a predisposition raises risk, it does not guarantee cancer — the remaining hits still have to happen. Second, most cancers (around 90 to 95 percent) are sporadic, not inherited, so a cancer with no family history is entirely ordinary and not a sign that something was 'passed down.'
A woman who inherits a faulty BRCA1 gene starts every cell one hit short of losing that tumor suppressor, so her lifetime risk of breast cancer is much higher and tends to appear at a younger age. Genetic testing can reveal this, allowing earlier screening — but it tells her about risk, not certainty.
Hereditary cancer means being born one 'hit' closer, not destined.
Most cancers (around 90 to 95 percent) are sporadic, not inherited; and inheriting a predisposition raises risk without guaranteeing cancer.