While most physicians today have discontinued the practice of making house calls, one professor at Harvard Medical School still makes them.

Well, sort of.

"We make mouse calls," proclaims a sign on the desk of the secretary of Philip Leder '56, Andrus professor of genetics and chair of the Medical School's Department of Genetics.

Leder's genetic research gained worldwide attention in 1988 when he became the first to obtain a patent on a genetically altered animal.

With the ability to inject a mouse egg with a gene that may lead to cancer, Leder says he and his staff of researchers can test various hypotheses about cancers.

By looking at whether or not the mouse's offspring develop cancer, Leder can learn what secondary factors influence the development of malignant tumors, he says.

Leder says that with the aid of the genetically altered--or transgenic--mice, he has discovered much about cancer that could not be learned from just studying tissue cultures.

"It is a disease which occurs in an organism," he says. "If you want to understand a disease this complex which occurs in a living organism, you have to study that organism."

Genetics and Cancer Linked

In the last decade, researchers have learned that genetics and genes are to a large measure at the root of the cancer problem, he says.

But this doesn't mean that humans necessarily inherit the propensity to develop cancer from their parents, or pass it on to their offspring, he adds.

"This is not genetics as we conventionally think about it," Leder says. "When cancer occurs, it reflects something that has gone wrong on the level of gene mutation."

In other words, some oncogenes--or cancer-causing genes--may be necessary, but not sufficient, for the development of malignant tumors, Leder says.

Mice Are Good Models

Determining which of these genes are involved in cancer is made especially easy by the use of the transgenic mice, Leder says.