How can molecular biology be used for the treatment and detection of cancer?

(N/A) $1$. Antibodies against cancer-specific antigens are used for the detection of certain cancers.
$2$. Techniques of molecular biology,such as gene sequencing and $PCR$,can be applied to detect genes in individuals with inherited susceptibility to certain cancers.
$3$. Identification of such genes,which predispose an individual to certain cancers,is very helpful in the prevention and early management of the disease.
$4$. Individuals identified with such genetic predispositions may be advised to avoid exposure to particular carcinogens to which they are susceptible,thereby reducing the risk of cancer development.