The Inheritability of Spontaneous Tumors of Specific Organs and of Specific Types in Mice: Studies in the Incidence and Inheritability of Spontaneous Tumors in Mice: Fifth Report

Abstract

During the past three years I have published from this laboratory a series of papers giving data and charts which demonstrate the persistent tendency toward the occurrence of spontaneous tumors in strains of mice where tumorous individuals have been bred in. (1) This persistence occurs when given the only two possible tests of heredity, namely, inbreeding and hybridization; and it occurs in every such strain where the offspring have lived to cancer age in sufficient numbers to make even a meager test. (2) On the other hand, certain strains of mice when given every possible test by the closest inbreeding and by hybridization with other proved non-cancerous strains have never produced a single case of tumor of any sort. And (3) into such proved non-tumorous strains of mice, cancer has been introduced by hybridizing them with proved tumor-bearing strains. From such crosses, in every case where the offspring have lived to cancer age in sufficient numbers to make a test, it has been possible to extract, on the one hand, strains which never produce cancer; and, on the other hand, strains which inevitably do produce cancer and which in turn carry it into every strain with which they are hybridized. Moreover, the behavior of spontaneous cancer in heredity is shown in these reports to be strikingly like that of a mendelian so-called “recessive,” such as albinism. A summation of the results in Chart 21 of the third report shows a very close approximation to the “mendelian expectation” for a recessive (3). At the same time control experiments were described, by which other possible causative factors for the transmission of spontaneous cancer have been eliminated (1, 3). It might be well to repeat at this time that the tumors reported are all spontaneous tumors, arising in the ordinary course of mouse life, without any artificial interference whatever in the nature of grafts, inoculations, or any other form of manipulation. The stock is kept under conditions of the most rigorous hygiene; and every effort is made to eliminate infections and to carry every individual to the greatest possible age. The housing, feeding, and every other detail in the life of the mice is identical in the tumor and in the non-tumor strains, thus eliminating these external conditions as a factor in the occurrence of cancer within certain strains and its absolute non-occurrence in certain other strains. It is an interesting point that during the ten years of the maintenance of this stock there has never been a severe epidemic of any type whatever, not even of intestinal or pulmonary infections, to which mice are easily subject. The routine which has been established in the laboratory in the matter of housing, food, reproduction, etc., has yielded a stock whose average age is far beyond the average age limit quoted for mice. Many individuals both in the tumor and in the non-tumor strains live to be from three to five years old. The strains are vigorously reproductive and bear inbreeding for many generations before they run out.