196 TEE SCIENTIFIC MONTHLY
��THE RELATION OP HEREDITY TO CANCER IN MAN
AND ANIMALS
bt c. c. little
CAXCMR C0KMIB8I0N OF RUtTABD UMIYBBSITZ
THE existence of hereditary tendencies or predispositions to cancer, in man, has been for years and still is a much debated question. In the face of a steadily increasing volume of evidence both pro and contra, not only laymen, but the medical profession as well are still of uncertain or divided opinions. Gradually, however, medical institutions have taken up the investigation of the problem until at present a con- siderable number of laboratories are engaged in experimental studies to determine the importance of heredity in the transmission of cancer. Be- cause of this fact it may be of interest to consider broadly the relation of present genetic methods to the problem of human cancer. We may do this in the hope of determining in advance, if possible, the necessary limitations in applying such methods to the problem in question.
Two main lines of research in genetics may contribute data which have a definite bearing on the question as to whether or not there are hereditary tendencies to cancer in man. The first of these is a study of family histories in human beings themselves; the second is the experi- mental study of inheritance in the lower mammals.
The value of any data obtained must obviously be based on its scien- tific accuracy and on its applicability to the problem under consideration. We mlBiy now briefly consider the obtainable data in the two branches of research indicated and apply to them the test of value, above mentioned.
All data involving several generations of human beings are of neces- sity, under our present methods, based at least partly on *^ hearsay*' evidence. The amount of data so obtained when compared with those ob- tained by direct observation will of course vary in different individual problems. It will, however, always be present as a source of fundamental inaccuracy.
There are many other minor, but none the less important, sources of error. Among these may be mentioned ignorance as to the exact cause of death or diagnoses based on clinical rather than autopsy data. Failure to give suflScient prominence to age, as an important factor, may further complicate the problem. Numerous similar conditions combine with those mentioned to make the data gathered from available sources en- tirely unreliable in determining the course of inherited tendencies to cancer in the human race.
The accuracy of the data obtained from experimental studies of the
�� �
