Dr. Ludwik Gross, who influenced cancer research by showing that viruses could cause cancers in animals, died on Monday at Montefiore Medical Center in the Bronx. He was 94 and lived in the Riverdale section of the Bronx.
The cause was stomach cancer, said his daughter, Dr. Augusta H. Gross.
Dr. Gross won an Albert and Mary Lasker Foundation prize in 1974 for his discovery of what became known as the Gross mouse leukemia virus. His work in the 1950’s, the Lasker jury said, opened the field of tumor virology in mammals and “laid the foundations for the subsequent discovery by others of cancer-inducing viruses in animals of various species ranging from rodents to the higher primates.”
Until 1951, scientists believed that mouse leukemia, and many other leukemias, were genetic diseases and not transmissible. Then Dr. Gross upset that dogma by showing that a virus caused mouse leukemia and could be passed naturally from generation to generation, mother to baby. For many years “there was considerable reluctance and often even frank hostility to accept” his findings, he wrote in Cancer Research, a scientific journal, in 1978.
For the half-century before Dr. Gross’s discovery, scientists had largely ignored the role of viruses in cancer even though, beginning in 1908, researchers had suggested a viral cause by transmitting leukemia and sarcomas in chickens. Over the next 30 years, scientists transmitted a type of kidney cancer prevalent in frogs in New England lakes to other frogs, and also transmitted breast cancer in mice through milk from mothers to their offspring.
Scientists called the mysterious factor responsible for transmitting the mouse breast cancer “milk influence,” not a virus, and used similarly meaningless terms to explain other transmissions now known to result from viruses.
In a sense, the ignorance was understandable: laboratory tools for detecting viruses were crude. But another problem was attitude. For decades, “investigators hesitated strongly to accept even as a working hypothesis the existence of a transmissible virus as the cause of tumors,” Dr. Gross wrote in a Cancer Research article in 1985.
Dr. Gross attributed that resistance to scientists’ penchant for following certain generally accepted concepts. “Research projects and experimental approaches radically different from such accepted concepts or theories were not only frowned upon,” he wrote, “but often resulted in the refusal of the necessary financial and logistical support needed by the investigator to carry out his proposed studies.”
Long before his discovery, Dr. Gross had theorized that a virus caused mouse leukemia. But for some time his many experiments at the Bronx Veterans Administration Hospital, where he was chief of cancer research, failed to find it. One day he heard a lecture by a scientist who was working on a different virus and who said he could show its harmful effects by injecting it into suckling mice, though not by injecting it into older mice.
So Dr. Gross injected material from leukemic mice into newborn mice of a strain known to be free of the leukemia, thus isolating a virus. He then showed that the virus was passed naturally through successive generations of mice to cause leukemia. “Thus,” Dr. Gross said, “not only in chickens but also in mammals,” he had demonstrated that leukemia often had a viral cause.
The “frank hostility” that Dr. Gross would describe years later gradually eased as he went on to show that radiation or a chemical could induce leukemia in an animal by activating a dormant virus. As time passed, other scientists developed vaccines against the feline leukemia virus in cats and a cancer known as Marek’s disease in chickens.
Scientists also proved his hypothesis that viruses could cause some human cancers. Among these viruses: two retroviruses, called HTLV-1 and HTLV-2, that cause rare types of leukemias and lymphomas; the Epstein-Barr virus, which is linked to Burkitt’s lymphoma and to cancer of the nose and the mouth, and the hepatitis B virus, which can lead to liver cancer.
Dr. Gross’s research led indirectly to the discovery of the AIDS virus, and some of his papers late in his career discussed how that virus was transmitted.
Ludwik Gross was born in Cracow on Sept. 11, 1904. Both parents were lawyers, and his father was a member of the Austro-Hungarian Parliament. After earning his medical degree at Jagiellonian University in Cracow in 1929, Dr. Gross trained in internal medicine for three years at St. Lazar General Hospital there.
In the 1930’s, he worked at the Pasteur Institute in Paris and wrote medical articles for Poland’s largest-circulation newspaper, IL Kuryen Codzieny in Cracow. It was while he was on a visit to Cracow in 1939 that Germany invaded Poland. A member of a prominent Jewish family, he escaped to Romania with a journalist friend just days ahead of the Nazis, who were hunting him and also closed the newspaper.
After immigrating to the United States in 1940, Dr. Gross worked at Jewish Hospital and Christ Hospital in Cincinnati, where he developed an interest in cancer research. In 1946, after service in the Army during World War II, he became chief of cancer research at the Bronx V.A. Hospital.
Dr. Gross the medical journalist had many letters published in The New York Times. In one, he opposed fluoridation of the water supply to prevent tooth decay, calling fluoride “an insidious poison, harmful, toxic and cumulative in its effect, even when ingested in minimal amounts.” He never changed his view.
Another letter criticized wholesale dealers who kept meat unwrapped in the trunks of their cars, often next to spare tires, as they made deliveries to butchers.
He urged prohibition of smoking on airline flights in yet another letter, published in 1958, more than three decades before the industry itself adopted the idea.
Dr. Gross’s textbook, “Oncogenic Viruses,” was a standard in the field. He was a member of the National Academy of Sciences, and his last scientific article, in 1998, appeared in the organization’s Proceedings.
In addition to his daughter, he leaves a brother, Felix, of Manhattan. Dr. Gross’s wife, the former Dorothy Nelson, died in 1988.