CANCER RESEARCH

Lake Wakatip Mail, Issue 3614, 18 November 1924, Page 2

CANCER RESEARCH

FURTHER STEPS TOWARDS KNOWLEDGE. The causes, as opposed to the cause, of cancer are gradually being elucidated (writes the medical correspondent of ‘The Times’). Thanks to a series of brilliant researches carried on within the last two decades, we are now in a position to say that cancer can be caused in certain am I mals by the X-rays, by applications of paraffins and tars, and by the ingestion of parasitic worms. To some of these researches, Dr Leitch and his co-workers at the Cancer Hospital have made valuable contributions. In the current issue of the ‘ British Medical Journal ’ an important addition to knowledge is described by them; Dr Leitch points out that in his own laboratory cancer has been produced by coal tar, tar extracts, pitch, soot, arsenic, shale oil and industrial oils derived from shale, by crude petroleums, lubricating oil, and by a tarry substance prepared from isoprene. Obviously, however, the proportion of. cancers arising from such agents (X-rays, tars, or worms) is small. A later research has been directed into causes of cancer operating within the body itself. The gall bladder was selected as the seat of experiment, and guinea pigs were chosen as experimental animals. They were not a very satisfactory choice—from one point of view—since the guinea pig has ever been known to develop any kind of carcinoma naturally. Operations were performed and a number of email gall etones were placed in the gall bladders of a number of guinea pigs. Others of the animals had small round stones placed in their gall bladders. In a number of instances true “glandular” type cancer developed. It would seem to follow that, in this animal at any rate, gall etones are able to set up cancer. Nor do they accomplish this by any special chemical in their composition, since ordinary pebbles are equally efficacious. The cause would seem to be ordinary mechanical irritation. The result is the more interesting that stones or “calculi” in other regions are not known to be associated with cancer, and that nobody, by animal experiment, has induced a cancer heretofore merely by mechanical irritation. A STEP FORWARD. Rash conclusions, however, cannot and must not be drawn. While mechanical irritation does cause cancer in the gall bladder of the guinea pig, there is no assurance that it will do this in other sites or in other animals. In all disease we have to consider the pathogenic agent on the one hand and the susceptible or refractory tissue on the other. Thus, if tar is applied to a mouse’s skin, a skin cancer will eventually develop, but no amount of tar application will cause cancer on a rat sor a guinea pig’s skin. Further, tar applied to the inside of the bowel in a mouse produces no cancer—i.e., this particular tissue is not vulnerable to this particular form of irritant. Ibis work breaks new ground, and is a clear step forward towards knowledge of the cancer problem. For the results achieved are quite new in four separate ways : (1) Ibis is the first time a carcinoma has ever been produced in a guinea pig, and that animal has never been known to develop any kind of carcinoma naturally. (2) It is the first demonstration that a mechanical irritant can produce cancer. (3) It is the first time a cancer of the glandular type has ever been produced experimentally. (4) Above all, it is the first demonstration that a pathological substance developed wholly within the living body—i.e., a gall stone—can produce cancer by prolonged irritation or injury.