Tests for Effects of Asbestos on Benzo Pyrene Carcinogenesis in the Respiratory Tract

Our plain-English summary of Tests for Effects of Asbestos on Benzo Pyrene Carcinogenesis in the Respiratory Tract, by L. Miller, W.E. Smith, S.W. Berliner (1965).

The study

• Authors: L. Miller, W.E. Smith, S.W. Berliner
• Published: Annals of the New York Academy of Sciences (1965)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This animal experiment tested whether asbestos increases the cancer-causing effect of benzo[a]pyrene in the airways of male golden Syrian hamsters. Benzo[a]pyrene is a carcinogen found in cigarette smoke. In the first experiment, 50 hamsters were split into five groups of ten. Four groups were given weekly injections into the windpipe for 25 weeks, though some animals died before finishing, and one group was left untreated. Among hamsters examined 173 to 214 days after the start, tumors were found in 3 of 5 given benzo[a]pyrene alone and in all 7 given it with chrysotile. No tumors appeared in hamsters given chrysotile alone, the suspending liquid alone, or nothing. The authors wrote that this suggested chrysotile promoted tumors, but there were too few animals to decide. In the second experiment, 80 hamsters were assigned 16 weekly injections of benzo[a]pyrene, half with amosite added; some died early. At 240 days, tumors were found in 8 of 27 survivors (29%) without amosite and in 5 of 19 (26%) with it. The authors concluded that amosite did not increase the tumor yield. Only tumors seen under a dissecting microscope and confirmed microscopically were counted, and the microscopic study was unfinished.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: animal experiment (two experiments with repeated intratracheal injections in hamsters)
• Who was studied: Male golden Syrian hamsters from Lakeview Hamster Colony, Newfield, N.J., one to two months old at the start; 50 in Experiment 1 (five groups of ten, one of them untreated controls) and 80 in Experiment 2 (two groups of 40)
• Exposure: Weekly intratracheal injections of benzo[a]pyrene (0.5 mg per injection) suspended in aqueous Tween 60. In Experiment 1 this was given with or without chrysotile (0.25 mg per injection; average fiber length 15 microns) for 25 weeks, with control groups given chrysotile alone, Tween 60 alone, or no treatment; some animals died before receiving the full course. In Experiment 2 it was given with or without amosite (2.5 mg per injection; average fiber length 17.6 microns) in a course of 16 injections; hamsters that survived the full course received 8 mg benzo[a]pyrene and, in the amosite group, 40 mg amosite.
• Main results:
  • Experiment 1, benzo[a]pyrene alone: respiratory tract tumors in 3 of 5 hamsters living 173 to 214 days, with 4 tumors in total (1.3 per tumor-bearing animal). The authors judged this dose too large for convenient measurement of any cocarcinogenic action of asbestos.
  • Experiment 1, benzo[a]pyrene plus chrysotile: tumors in each of the 7 hamsters examined in the same period. The number of tumors per tumor-bearing animal and the size of the tumors were greater than with benzo[a]pyrene alone, and the most malignant tumors were in this group.
  • Experiment 1, control groups: no tumors in hamsters given chrysotile alone (0 of 6 surviving beyond 173 days), the Tween 60 solvent alone (0 of 10), or no treatment (0 of 10).
  • Experiment 2, 8 mg benzo[a]pyrene alone: of 40 hamsters at the start, 27 survived to 240 days and 8 had tumors (29%).
  • Experiment 2, 8 mg benzo[a]pyrene plus 40 mg amosite: of 40 hamsters at the start, 19 survived to the scheduled sacrifice and 5 had tumors (26%), all single papillomas. The authors found no evidence of a promoting action of amosite.
  • Experiment 2, benzo[a]pyrene groups: tumors were found in 7 of 11 hamsters examined between 201 and 217 days but in only 8 of 27 examined on the 240th day (approximately 64 versus 30 per cent).
• The authors' conclusion: The authors concluded that adding chrysotile gave results consistent with the hypothesis that it promoted benzo[a]pyrene carcinogenesis in the respiratory tract, and that adding amosite did not increase the tumor yield. They also concluded that after a limited series of benzo[a]pyrene injections the tumor yield decreased with time after exposure stopped, which they noted was of interest in relation to lung cancer risk in smokers who quit.
• Limitations the authors state:
  • Histological study of all specimens was not completed, so only tumors detected in gross specimens and confirmed histologically were tabulated.
  • In Experiment 1 the numbers of animals were too small to permit a decision about promotion by chrysotile.
  • In Experiment 2, deaths before 240 days were difficult to compare because the benzo[a]pyrene plus amosite group did not live as long as the benzo[a]pyrene group.
  • An outbreak of an endemic hamster disease ('wet tail') caused some deaths in both groups of Experiment 2.

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenesis, Chrysotile, Amosite.

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