Why do human cancer death rates increase with age? A new method of analysis of the biology of cancer.
1. Cancers, viewed as escape from the normal "contact inhibition" of cells in tissues, can be considered to start at some given time and then to require a period of incubation before they cause death. The probability of a start may depend on age, described by a start function. The incubation period may be described by a lethality function of the period between start and the age at which death rates are measured. 2. It can be shown that, provided the loss of tumour-bearers (where cancer has started) in the population by deaths from other causes than cancer is in the same ratio as the loss of total population, the differential curve (dR/dA) of the rate versus age curves must give the product of these two functions (start function X lethality function). 3. The differential curves dR/dA for major sites of cancers are examined for WHO data on  deaths. The differential curves prove to be well described by normal Gaussian curves. The presence of more than one type of tumour or of physiological environment, included in a single category, is shown by multiple peaks in the differential curves. The outstanding exception is tumours of the "brain and other CNS" where the rate curve itself is Gaussian. 4. The results are consistent with a start rate that is random and independent of age (not exceeding three per 1,000 per year for the commonest tumour), and an astonishingly long incubation period of at least 20-50 years. For most sites, the curves indicate that from 20 to 40% of the cancers that have started do not cause death, because other causes supervene. 5. The implications as to the possibilities of control of cancer and of the relevance of experimental cancer research are discussed.
D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging; D000531:Altitude; D001932:Brain Neoplasms / Q000401:mortality; D001943:Breast Neoplasms / Q000401:mortality; D002648:Child; D002675:Child, Preschool; D003260:Contact Inhibition; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007414:Intestinal Neoplasms / Q000401:mortality; D007938:Leukemia / Q000401:mortality; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009369:Neoplasms / Q000209:etiology / Q000401:mortality*; D010190:Pancreatic Neoplasms / Q000401:mortality; D011336:Probability; D011471:Prostatic Neoplasms / Q000401:mortality; D013274:Stomach Neoplasms / Q000401:mortality; D001749:Urinary Bladder Neoplasms / Q000401:mortality