The risk of cancer therapy.

Survival times of treated cancer patients are distributed lognormally. This density function exhibits a peak accompanied by a long tail which asymptotically approaches the abscissa. The lognormal conditional failure rate, known also as force of mortality, which describes the chances of a patient remaining alive, initially climbs, to decline at a later phase. This decline is observable in all survival curves of the "Fourth report on the end results of cancer" in the U.S., and has been documented also by other epidemiological surveys. It implies that with the progression of the disease the chances of the average patient to survive improve. This pattern indicates the existence of a mechanism which is assumed to be associated with neoplasia, and assists the patient to withstand cancer. The initial rise of the force of mortality is assumed here to be associated with cancer treatment which undermines the beneficial role of neoplasia.