title: [Background data of spontaneous tumors in F344/DuCrlCrlj rats].
abstract: BACKGROUND
  We investigated the 2-year survival rate and incidence of spontaneous tumors in F344/DuCrlCrlj rats used in carcinogenicity studies of chemical substances. Records for animals used in the control groups of carcinogenicity studies which were conducted during the last 10 years were obtained from the database of the Japan Bioassay Research Center (JBRC). Six hundred ninety-nine males and 550 females were used in 14 and 11 inhalation studies, respectively, and 500 animals of each sex were used in 10 male and 10 female oral studies.
  
  
  METHODS
  In each study, SPF (specific pathogen free) animals were housed for 2 years (104 weeks) as control groups in the carcinogenicity studies. All animals underwent necropsy and histopathological examination. Each study was conducted in accordance with the Good Laboratory Practice.
  
  
  RESULTS
  The incidence of interstitial cell tumors was highest in both inhalation studies and oral studies (inhalation studies 86.1%, oral studies 68.6%). Tumors which had an incidence of 6% or higher were adenoma of the pituitary, C-cell adenoma of the thyroid, and mononuclear cell leukemia (LGL leukemia) of the spleen in male and female rats; fibroma of the subcutaneous tissue, adrenal pheochromocytoma, and islet cell adenoma of the pancreas in male rats; and endometrial stromal polyps and fibroadenoma of the mammary gland in female rats. Tumors other than the above had rare incidence rates. A clear difference in the incidence of spontaneous tumors was not observed between the inhalation and oral studies. The incidences of spontaneous tumors in control groups of previous oral studies are similar to our findings. There are no other reports of the spontaneous tumor incidence in the control groups of inhalation studies using F344/DuCrlCrlj rats. The 2-year survival rate was about 77% in both the inhalation and oral studies, and a gender difference was not observed. The F344/DuCrlCrlj rats used at JBRC had a higher 2-year survival rate than F344/N rats. This difference is possibly due to the low incidence of LGL leukemia in the F344/DuCrlCrlj rat.
  
  
  CONCLUSIONS
  The incidences of spontaneous tumors in F344/DuCrlCrlj rats used in control groups of both inhalation and oral studies during the last 10 years at JBRC are similar to each other and similar to those reported in other studies. This is the first report on the incidence of spontaneous tumors in inhalation studies and contributes to the toxicological evaluation of studies using F344/DuCrlCrlj rats.
authors.affiliation: Japan Bioassay Research Center, Japan Industrial Safety and Health Association, 2445, Hirasawa, Hadano, Kanagawa 257-0015, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Takanobu
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Aiso
authors.forename: Yumi
authors.initials: Y
authors.lastname: Umeda
authors.forename: Hideki
authors.initials: H
authors.lastname: Senoh
authors.forename: Misae
authors.initials: M
authors.lastname: Saito
authors.forename: Taku
authors.initials: T
authors.lastname: Katagiri
authors.forename: Naoki
authors.initials: N
authors.lastname: Ikawa
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Mine
authors.forename: Makoto
authors.initials: M
authors.lastname: Take
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Haresaku
authors.forename: Michiharu
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Shoji
authors.initials: S
authors.lastname: Fukushima
mesh_terms: D000280:Administration, Inhalation; D000284:Administration, Oral; D000818:Animals; D000830:Animals, Laboratory; D015197:Carcinogenicity Tests / Q000379:methods; D002273:Carcinogens / Q000008:administration & dosage / Q000633:toxicity; D005260:Female; D008297:Male; D009369:Neoplasms / Q000139:chemically induced / Q000453:epidemiology* / Q000473:pathology / Q000662:veterinary*; D051381:Rats; D011916:Rats, Inbred F344; D012376:Rodent Diseases / Q000139:chemically induced / Q000453:epidemiology* / Q000473:pathology; D013047:Specific Pathogen-Free Organisms; D015996:Survival Rate; D013997:Time Factors
chemical_list: D002273:Carcinogens