title: Environmental factors affect colon carcinoma and rectal carcinoma in men and women differently.
abstract: OBJECTIVE
  Colon cancer is thought to be more closely associated with environmental factors than rectal cancer, but evidence is currently insufficient. We examined whether there are differences in the degree of environmental effect on colon cancer and rectal cancer in Japan.
  
  
  METHODS
  We performed a birth cohort analysis for colon and rectal cancers using Japanese vital statistics from 1950 to 1998 and analyzed time trends by cancer site and gender.
  
  
  RESULTS
  The mean annual increase in age-adjusted mortality rate from colon cancer was greater than that from rectal cancer and was greater in men than in women. In men left colon cancer showed the greatest rate of increase whereas cancer of the right colon showed only a slight change. Although left colon cancer rapidly increased until the middle 1980s and thereafter showed no change, right colon cancer showed no change until the middle 1980s and thereafter rapidly increased in men. However, the rates of increase in left colon cancer were greater than those in right colon cancer until the middle 1980s, after which a reversal in trend was seen in women. Birth cohort analysis indicates that for all cohorts the mortality rates at the same age were higher in the recent cohorts than in the previous ones. This trend was more marked for colon cancer than for rectal cancer and was stronger among men than among women.
  
  
  CONCLUSIONS
  Colon cancer is more closely associated than rectal cancer with environmental factors, and this association is more pronounced in men than in women. Consequently cancers at these two sites should not be combined in studies of the role of lifestyle factors in causing these neoplasms. Furthermore, the causes of these diseases may differ in men and women.
authors.affiliation: Department of Hygiene, Hirosaki University School of Medicine, 5 Zaifu-cho, 036-8562, Hirosaki, Japan. nakaji@cc.hirosaki-u.ac.jp
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Nakaji
authors.forename: Takashi
authors.initials: T
authors.lastname: Umeda
authors.forename: Tadashi
authors.initials: T
authors.lastname: Shimoyama
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sugawara
authors.forename: Ken
authors.initials: K
authors.lastname: Tamura
authors.forename: Shinsaku
authors.initials: S
authors.lastname: Fukuda
authors.forename: Juichi
authors.initials: J
authors.lastname: Sakamoto
authors.forename: Stefano
authors.initials: S
authors.lastname: Parodi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma / Q000209:etiology* / Q000401:mortality* / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003110:Colonic Neoplasms / Q000209:etiology* / Q000401:mortality* / Q000503:physiopathology; D004777:Environment; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012004:Rectal Neoplasms / Q000150:complications* / Q000453:epidemiology; D012307:Risk Factors; D012737:Sex Factors