Chemotherapy – Introduction

The object of chemotherapy, as is true of all cancer therapies, is to kill cancerous cells without doing significant damage to normal cells in the surrounding tissue. As discussed in earlier posts, radiation therapy attempts to do this with targeted beams of energy radiation (cf my May 22, 2009 post). Surgery physically removes cancerous cells, whenever possible using minimally invasive procedures, such as video assisted thoracic surgery (VATS).

At its most basic level, all cancer is dysfunctional cellular mutation; that is, cell mutation which produces negative consequences. Until relatively recently, chemotherapy has been limited to the use of drugs which do not discriminate well between cancerous and non-cancerous cells. The results from the Human Genome Project are now contributing to the development of more targeted approaches for chemotherapy, allowing potential intervention at the sub-cellular level (DNA/RNA) to inhibit further mutation or induce cell death in cancerous cells by interrupting its growth cycle.

All cells go through four phases, referred to as the “cell cycle,” G1, S, G2, and M. G1 is most active in protein synthesis, during which few chemotherapy agents are effective. DNA replication is most active during the S phase, during which the cell is highly sensitive to some chemotherapy drugs. During G2, RNA is most active and some protein is formed. The M phase is when cell division (mitosis) occurs.

Consequently, many of the new approaches involve DNA modification of destruction. However, the human body has its own defenses against DNA damage, which work to repair damage, whether its from the cancer itself or a well-meant attempt to kill cancerous cells. The result is that, while the chemical intervention may kill the cancerous cell, it may also overwhelm the immune system, with its attendant risk of infections, or so stimulate the immune system that it produces an auto-immune response with risks, such as lupus or rheumatoid arthritis. The challenge of chemotherapy, as always, is to get the right drug, to the right cell, in the right amount, at the right time.

More about how that is happening later.