Immunologic
Escape
and
Immunotheraphy
In spite of immune surveillance, tumors occur in normal individuals because tumor cells escape destruction. Several theories are put to explain this immunologic escape. For instance, (i) individuals learn to tolerate tumor cells before' immune competence has developed and then express the tumor later in life, (ii) that majority of cancer cells are destroyed by killer cells, but that rapidly growing variants emerge and outpace the immune system, (iii) that tumor antigens elicit antibodies that protect against the killer cells, (iv) that tumor cells release substances that suppress the immune system.
