From 1974 to 1990, King carried out years of painstaking research, seeking a genetic marker, an identifiable piece of genetic material, that tended to accompany the presence of breast cancer in families. For much of that time, the predominant theory was that cancer was viral. Most scientists disregarded or attacked her ideas. The idea that genetic patterns could be linked to the incidence of complex diseases was considered an unlikely long shot. Genetics had been recognized as significant in diseases with a simple genetic tie, such as Huntington's disease, cystic fibrosis, and sickle-cell anemia, but researchers were skeptical about the usefulness of genetics in studying more common and complex diseases involving both multiple genetic factors and environmental influences. King sometimes worried that she was going down a blind alley in trying to study the interplay of genetics with a complex human disease.