Apoptosis includes all mechanisms, connected with programmed cell death and with mechanisms which control cell proliferation and its ability to repair damaged DNA.
Why a process of apoptosis takes place in our organisms? It’s crucial because this process removes non-functional cells physiologically, it’s induced by some xenobiotics (drugs) which are the reason for oxidative stress and that can alter mitochondrial activity. After that death receptors are activated and caspase enzymes as well.
This process is very effective; cell which is meant to be destroyed is marked and that is a signal which shouts like “eat me”. Apoptosis produces cell fragments called apoptotic bodies and they are then removed. Apoptosis is controlled by our system; on the other hand, necrosis isn’t.
This process is effective but can sometimes fail – cancer cells. Those cells are under influence of uncontrolled cell proliferation which is not well regulated by apoptosis. In other words, apoptosis is insufficient in those cases. However, that is one of the reasons, there can be also changes in signalisation pathways etc.
We should not forget that there are drugs, chemicals and toxins which induce or even inhibit apoptosis: COX-2 inhibitors, cyclosporin A, menadione, etc. Apoptosis can be the main mechanism of action or just an adverse effect. I provided some links, click if you’re interested.