Par-4: how far will it go?
The mainstay of cancer treatment typically includes surgery, chemotherapy, and radiation. If cancer is confined to one area, surgery alone can be curative, although it is often combined with adjuvant therapy (1). Radiation is limited to treatment of cells within the scope of the radiation beam, although radio immunotherapy has enhanced radiation therapy particularly in B-cell lymphomas (2). Chemotherapy has a number of forms, including systemically toxic drugs and both drugs and antibodies targeted to specific proteins that are driving the growth of the cancer cells. Chemotherapy can be used to treat systemically both visible and occult cancer cells. However, therapy resistance in tumors is a continuing problem for patients and oncologists alike despite an aggressive treatment regimen. In some cases, early mutations give resistance to tumors, or to a sub-population of tumor cells within a heterogeneous tumor, even prior to treatment. In this case treatment can cause death to sensitive cells allowing the few resistant cells to become the dominant population and lead to tumor recurrence. On the other hand, tumors that initially respond to treatment often become resistant over time as new mutations develop that allow cells to evade death. Such resistance, which may lead to multi-drug resistance, results in tumor recurrence and, ultimately, death (3).