December 21, 2016

Life span and cancer mortality in the Beagle dog and humans

Roy E. Albert, Stephen A. Benjamin, Rakesh Shukla, Elsevier, Colorado State University,1994

the question this study is trying to answer is to what extent is there a linkage between life span and cancer mortality in Beagle dogs and humans. The question is worth answering because most spontaneous cancers occur in the latter part of the life span in mammals, and the tumor response to carcinogens is more rapid in animals with shorter life spans. So far, the comparison of the development of tumors among species that have different life spans is limited because most studies in animals have been done on rodents. They hypothesized age would have a significant effect on beagles that is similar to humans. I predicted that as the dogs approached their final years the rates of cancer mortality would increase significantly. The dogs were allowed to live out their full lifespans and they were kept according to the NIH Guide for the Care and Use of Laboratory Animals. The dogs were fed a controlled diet that was changed after 1 year of age. A total of 1680 animals were used in the full experiment. Of these, there were 287 sham irradiated dogs, 143 males and 144 females, that served as controls and the rest were exposed to whole body gamma radiation. Each dog was given a complete physical examination once a year and with higher frequency if there was an illness found. Upon death, each dog was given a necropsy and the cause of death was examined. Cancer mortality in the Beagles was compared with that for white U.S. and Japanese men and women in 1977. The year 1977 was chosen because it was the midpoint of the Beagle study. About 60% of the cancers that caused death in male beagles were lymphomas and sarcoma. Mammary, lymphoma, and sarcoma accounted for 73% of cancer deaths in female beagles. Over half of the cancers in men are accounted for by the lung, colon/rectum and prostate, and in women, the lung, breast, and colon/rectum. Leukemia/lymphoma and sarcomas, in contrast to the dogs, was a small fraction of human cancer mortality. Japanese differ from U.S. whites in having a higher rate of stomach cancer and a lower incidence of large bowel cancer and leukemia in both sexes, and a lower incidence of breast cancer in women. The data presented in the study demonstrated that the association between cancer and aging is close in the Beagle dog and humans when examined in terms of cancer mortality.

 There are different ways humans and dogs are affected by the environment. Humans move around the world more freely than Beagles and are exposed to more carcinogens. The Beagles lived their entire lifetime inside a laboratory environment in a rural area where the level of air pollution was relatively low. Environmental factors are associated with cancer since high carcinogen exposures do cause cancer in humans, and migrants assume the cancer patterns of their host countries. A substantial proportion of cancer in humans happens in organs that are exposed to the environment, particularly the mucosa of the respiratory and gastro-intestinal tracts. By contrast, very few cancers occurred in these locations in Beagles, which suggests that cancer mortality in Beagles was not significantly caused by ingested or inhaled carcinogens.

Reviewed by Jonathan Guzman