Because of his strong background in genetics Dr. Lynch had the idea to look at cancer from a genetics perspective (he postulated that cancer could be hereditary) rather than from an environmental point of view (which at the time was the only acceptable cause for cancer in the medical circles). This idea became the main focus of his research for years to come.
His painstaking record-keeping and compilations of family medical history data led him to identify cancer syndromes and their patterns of inheritance through generations of extended families. In the course of his work, Dr. Lynch developed what are today regarded as the cardinal principles of cancer genetics: early age of onset of the disease, specific pattern of multiple primary cancers, and Mendelian patterns of inheritance in hundreds of extended families worldwide.