Blood cancers and many solid cancers have already spread to the entire body even at the time of their detection. Even when a tumor like breast cancer is detected in an apparently localised early stage, many a times, the disease comes back if surgery alone is performed for its treatment. It is assumed that even in some of the earliest tumors, some cancer cells might have spread to distant sites where they remain dormantly for an indefinite time period before eventually relapsing. That is why we need to treat the disease with medicines that can reach each and every site in our system- this forms the basis of systemic treatment for cancers.
Over the last 50 years, tremendous advances have happened in our understanding of many cancers. Many paediatric solid tumors and leukemias are now eminently curable with chemotherapy. Systemic chemotherapy has also been established as important components of treatment of cancers like testicular cancer, breast cancer, ovarian cancer and colonic cancers.
The biggest challenge about systemic chemotherapy lies in its nonselective nature. That is, the drug cannot distinguish between cancer cells and many normal rapidly dividing cells..
Most of the dreaded complications of chemotherapy like hairloss, decreased blood cell counts and life threatening infections are due to this nonselective effects on normal cells. But with recent advances in drug delivery and the introduction of the whole new gamut of more selective targeted agents, chemotherapy has evolved into a much more tolerable treatment
Autologous and allogenic bone marrow transplants have also extended the limits of modern day medical oncology in the management of blood diseases like leukemias and myeloma.