FEDERAL, SECURITY AGENCY

U.S. PUBLIC HEALTH SERVICE
NATIONAL INSTITUTE OF HEALTH
BETHESDA 14, MARYLAND

 

IN REPLYING, ADDRESS THE

Refer to: NC-RB<-BS July 10, 1952

Dr. Joshua Lederberg
Department of Genetics
University of Wisconsin
Madison 6, Wisconsin

Dear Doctor Lederberg:

I am extremely sorry that it has been
so long before I answered your note of June 6.

At that time we were in the throes of
not only preparing our annual reports, but also
preparing for a new fiscal year.

If the attached citation does not meet
your needs, I should be glad to try again.

Cordially yours,

Ub. ble

He Be Andervont

Attachment.
Inbreeding of mice produced some strains in which
many breeding females developed breast cancer and others in
which the incidence of these tumors was very lowe Hybridiza-
tion of these strains and foster nursing revealed that mother's
milk contained an agent of prime importance in the occurrence
of breast cancer. Thus, the establishment of inbred strains
of mice for use in cancer research was fully justified.

The mouse mammary tumor agent has many properties
in common with known viruses but also possesses certain unique
properties which can be used to ex» lore the virus etiology
of cancer. These properties are its long latent period, its
presence in inbred animals and its transmission from generation
to generation.

This agent is ingested during the first few hours
of life but the resultant tumor does not arise until middle
or late life. During this time the animal grows normally,
reproduces and shows no symptom of carrying the agent. There

(2loge  avesciafcan
is, in all probability, a (symbiotic? relationship between the
agent and the mammary gland cells of certain inbred strains.
Studies of this relationship may throw some light on the role
of latent or masked viruses in the cancer problem. Indeed,
the primary objective of investigations dealing with the

virus etiology of cancer is to expose or unmask latent viruses.