A white woman in rubber gloves prepares a sample.

The Search for Cancer Viruses, 1966

Circulating Now welcomes guest blogger Robin Wolfe Scheffler, the Leo Marx Career Development Assistant Professor in the Program in Science, Technology, and Society at the Massachusetts Institute of Technology. In his research for his just-released book, A Contagious Cause: The American Hunt for Cancer Viruses and the Rise of Molecular Medicine (University of Chicago Press, 2019), he made extensive use of the collections of the National Library of Medicine. Today he uses that expertise to guide us through one of the films held by the Library on the “Search for Cancer Viruses.”

A short typwritten letter.
Ludwik Gross to Dr. A. C. Denny (Wyeth, Inc.), March 8, 1945
National Library of Medicine MS C 504
Ludwik Gross Papers, box 3, folder 59

The mid-twentieth century theory that there might be a viral cause of cancer was the latest iteration of the long running belief that cancer was contagious. In the early decades of the twentieth century, when the field of virology was not yet fully developed, this theory attracted widespread skepticism. Doctors pointed out that they did not catch cancer from their patients. Scientists such as Ludwik Gross, whose study of leukemia in mice played an important role in reviving the theory of viral carcinogenesis in the 1950s, were at first considered fringe figures for their conviction that a virus might transmit cancer from generation to generation. Gross, however, was deadly serious. Because mouse nursing studies from the 1930s suggested that a viral “milk factor” could pass mammary tumors from mother to daughter, he considered raising his own infant daughter on formula in order to avoid the risk of intergenerational transfer of a possible human breast cancer virus. Following his findings and other advances in virology, by the 1960s the possibility that human cancer had viral causes seemed chillingly plausible.

A one page typwritten letter.
Letter from Stuart M. Sessoms (Assistant Director National Cancer Institute), July 11, 1958
National Library of Medicine MS C 360
Sarah Stewart Papers, box 2, folder Correspondence S 1958

A 1966 film by the U.S. Public Health Service, took the public inside The Search for Cancer Viruses, showcasing the not only the difficulties associated with this search, but also the sense of hope that made it appear worthwhile. Scientists at the National Cancer Institute who appeared in the film, such as Sarah Stewart, whose work confirmed the existence of cancer viruses in mice and extended this work to other rodent species, had initially been skeptical of human cancer viruses. In the late 1950s, Stewart turned away citizens writing to volunteer themselves for “experimental research” to demonstrate similar connections in humans, cautioning that virus studies were “not yet ready for application to human beings.”

Despite restraint from virologists, the opening of “Search for Cancer Viruses” gives a sense of why the National Cancer Institute grew more willing to place scientific doubts aside and pursue the development of a leukemia vaccine. The film opens with a shot of a young girl, Sandra, riding her bike in a suburban neighborhood, revealing that she “is a child apart. She has leukemia.” We go with her into the hospital where the narrator raises the viral theory of leukemia and asks, “but can scientists prove that viruses are a cause of cancer?”

Using Sandra to frame the search for a leukemia virus reflected the potent association of children, cancer, and vaccination in the aftermath of the polio vaccine campaigns of the 1950s. Both fundraisers and administrators at the National Cancer Institute realized that presenting cancer as a children’s disease promoted far more urgency for cancer research than when it was framed as a disease which threatened adults. In particular, the opening of the film recalled a notorious cluster of potentially infectious leukemia reported among the children of the Chicago suburb of Niles, Illinois in 1961.

Following Sandra to the Roswell Park Memorial Institute outside of Buffalo, New York, the film stepped back to explain the challenges that that faced scientists when they sought to demonstrate that viruses caused cancer. The filmmakers highlighted new technologies that made viruses visible in the same way as bacteria had been studied in the laboratory, especially electron microscopy and ultracentrifugation.


One of the challenges facing virology was that the immune system of experimental animals would often suppress viral activity. Sarah Stewart explained how she used infant mice, which have a very weak immune system, to demonstrate that viral infection could cause mouse leukemia following Koch’s postulates. However, the film assured its viewers, these methods could not be practiced in the case of experimentally proving the viral origins of human cancer—infecting healthy humans with potential cancer viruses would be unethical.

Building infrastructure to allow numerous scientists to participate in cancer virus research was a vital element of the approach to the search for a cancer vaccine adopted by the National Cancer Institute’s Special Virus Leukemia Program. For researchers at smaller laboratories, isolating and cultivating candidate human cancer viruses was among the most expensive barriers to joining the search. James Grace, the director of Roswell Park and an advisor to the Program, collected and cultured samples of possible cancer viruses for further study and distribution. Grace led viewers through one of the facilities supported by the National Cancer Institute, emphasizing their ability to mass produce viruses and ship them safely to laboratories around the country in specialized biohazard containers.

Even though Grace was at pains to underline that cancer was not contagious in the sense of measles or mumps, in the film’s penultimate scene, where he spoke with Sandra ’s mother regarding a “cure” for cancer, he held forth the hope that immunization against cancer would become a possibility. Since “the human is a member of the animal kingdom,” Grace thought it unlikely that they would prove the exception to the growing number of leukemia viruses identified in animals ranging from mice to monkeys. This rhetoric reflected the growing authority of experimental medicine and its faith that animal studies were accurate guides to human disease.

The close of the film returned to Sandra’s suburban neighborhood, leaving viewers with the hopeful message that “Many scientists like Dr. Stewart and Dr. Grace believe that” vaccination against cancer was a possibility, and with it the “long-awaited cure for cancer.”

With the declaration of President Richard Nixon’s “War on Cancer” in the 1970s, the Special Virus Leukemia Program grew to encompass the development of vaccines against all kinds of cancers. It eventually spent more than the Human Genome Project on its search for human cancer viruses. Throughout, it was driven by the mission of not only understanding cancer’s viral causes but using them to provide a cure for cancer. The conjoint images of threatened children and laboratory science presented by “The Search for Cancer Viruses” film were an important part of the rhetorical push to advance this vast research program.

Watch or download The Search for Cancer Viruses on NLM Digital Collections.


  1. Cancer is indeed the terrible thing and throughout the years we are working towards the progress to tackle the issue, but I think we are still behind my major steps to kill this thing ones it for all, anyhow Thanks for sharing the research Robin Wolfe 🙂

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