Tumour initiation by natural and contaminating asbestos oils

Our plain-English summary of Tumour initiation by natural and contaminating asbestos oils, by F.J. Roe, M.A. Walters, J.S. Harington (International Journal of Cancer, 1966).

The study

• Authors: F.J. Roe, M.A. Walters, J.S. Harington
• Journal: International Journal of Cancer
• Published: 1966;1(5):491-5
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Oils are present "naturally" in crocidolite and amosite asbestos. During processing, transport and storage, asbestos tends to be contaminated with other oils, including jute oil. Large commercial samples of crocidolite and amosite were extracted, by means of specially purified solvents, to remove both primary and contaminating oils. The latter were tested for tumour-initiating activity by twice-weekly application to the dorsal skin of mice alternating with once-weekly application of the tumour-promoting agent, croton oil. Significantly more papillomas and, in the case of amosite oil, carcinomas, arose in response to treatment with asbestos oil plus croton oil than in response to croton oil only. The tumour-initiating response was weak but reasons are given for not rejecting the possibility that the oils play a significant role in the induction of cancer by asbestos.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

In this animal experiment in London, the authors extracted oils from about 45 kg each of crocidolite and amosite asbestos. The extracts mixed oils naturally present in the fibres with oils, such as jute oil, that can contaminate asbestos during processing and storage; the two kinds could not be told apart. Three groups of 30 male mice had their backs painted twice weekly for 12 weeks with crocidolite oil, amosite oil, or acetone (the controls). All three groups also received croton oil, a tumour promoter, once weekly for up to 45 weeks. This tested only whether the oils could start (initiate) skin tumours. Mice given crocidolite oil developed significantly more skin tumours than controls (P less than 0.01). In the amosite oil group the difference from controls was even more significant, and four mice had skin carcinomas. Two of 29 control mice developed papillomas. The authors concluded that both oils had tumour-initiating activity but that the response was weak. They found it difficult to believe the oils play a major role in cancer caused by asbestos, without rejecting a possible role. Only one sample of each oil was tested.

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: mouse skin tumour-initiation test (oil applications followed by the promoter croton oil), with an acetone-plus-croton-oil control group
• Who was studied: 90 male Chester Beatty (CB) strain mice, 7 to 8 weeks old, bred at the Chester Beatty Research Institute, London. They were randomly divided into three groups of 30.
• Exposure: Oils were extracted with purified petroleum ether from mixtures of virgin and commercial crocidolite and amosite fibres. The extracts contained both natural and contaminating oils. Undiluted crocidolite oil or amosite oil (0.3 ml per application) was painted twice weekly for 12 weeks, 24 applications totalling 7.2 ml; controls received the same volume of acetone. All groups also received 0.1% croton oil once weekly for up to 45 weeks.
• Main results:
  • Mice given crocidolite oil plus croton oil developed significantly more skin tumours than controls given acetone plus croton oil (P less than 0.01)
  • In the amosite oil plus croton oil group the difference from controls was even more significant, and four mice had skin carcinomas. The P value is printed in garbled form as 'P<O.OOl', which most likely reads P less than 0.001.
  • One of the four skin carcinomas in the amosite oil group had spread to the axillary gland
  • In the control group (croton oil plus acetone), two out of 29 mice developed papillomas, after 31 and 40 weeks
  • The earliest papilloma appeared after 13 weeks, in the amosite oil plus croton oil group
  • As read from the table, 66.6% of survivors in the amosite oil group developed skin tumours, with 40 skin tumours in total, 4 of them malignant
  • As read from the table, 51.7% of survivors in the crocidolite oil group developed skin tumours, with 36 skin tumours in total, none malignant; the first skin tumour appeared at 17 weeks
  • At the end of the experiment 21 mice were alive in Group 1 (crocidolite oil), 23 in Group 2 (amosite oil) and 25 in Group 3 (controls)
  • The authors did not consider the malignant lymphomas, hepatomas and lung adenomas seen in Groups 1 and 2 significant, because CB stock mice are prone to these tumours
  • More polycyclic hydrocarbons were detected in the amosite oil than in the crocidolite oil
  • The authors concluded that both oils possess tumour-initiating activity
  • The authors described the tumour response to the two oils as weak compared with agents such as 7,12-dimethylbenz[a]anthracene
• The authors' conclusion: The authors concluded that both oils have tumour-initiating activity. Because the effect was weak and the oils are minor constituents of asbestos, they found it difficult to believe the oils play a major role in cancer caused by asbestos. They gave reasons for not rejecting a possible role, such as the enhancing effect that low-reactivity substances can have on small amounts of carcinogens.
• Limitations the authors state:
  • Only one batch of crocidolite and one batch of amosite could be examined
  • The degree of contamination with jute oil and other secondary oils could not be assessed, and natural and contaminating oils could not be distinguished in the extracted material
  • There was not enough material to test the oils for complete carcinogenicity (or tumour-promoting activity); only initiation was tested
  • The authors could not know how representative the samples were in oil content or in concentration of carcinogenic polycyclic hydrocarbons

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Amosite, Carcinoma.

Related studies

• Studies of carcinogenesis of asbestos fibers and their natural oils — J.S. Harington, F.J. Roe (1965)
• Initiation-promotion versus complete skin carcinogenesis in mice: importance of dark basal keratinocytes (stem cells) — T.J. Slaga, A.J. Klein-Szanto (1983)
• Phosphatide composition of normal, hyperplastic and malignant squamous epithelium — C. Carruthers (1966)
• Contaminating organic material in asbestos — B.T. Commins, G.W. Gibbs (1969)
• Asbestos-induced tumors in White Leghorn fowls — P.R. Peacock, A. Peacock (1965)
• The INTEROCC case-control study: risk of meningioma and occupational exposure to selected combustion products, dusts and other chemical agents — D.M. McElvenny, M. van Tongeren, et al. (2018)

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