[4] After the war ended she enrolled as a graduate student in the Department of Microbiology at Yale, where she received her PhD in 1950 with a thesis on the effects of sodium salicylate (aspirin) on antigen-antibody reactions[5] During her time at Yale she frequently traveled to New York to consult with Elvin Kabat and Michael Heidelberger, eminent immunologists at Columbia.

Once, when looking through an unused electron microscope at the university, they decided to look at fine structures within the cells of the Ehrlich ascites carcinoma, a commonly used model for cancer research.

It was this incident that sparked Friend's interest in the possibility of cancer being caused by viruses, which became a main focus of her research.

In 1966 she accepted a position as professor and director of the Center for Experimental Cell Biology at The Mount Sinai Hospital.

During her lifetime she was president of the Harvey Society, the American Association for Cancer Research and the New York Academy of Sciences and was the first woman to do so.