These historical observations suggested that cervical cancer could be caused by a sexually transmitted agent. Initial research in the 1940s and 1950s attributed cervical cancer to smegma (e.g. Heins "et al." 1958). During the 1960s and 1970s it was suspected that infection with herpes simplex virus was the cause of the disease. In summary, HSV was seen as a likely cause because it is known to survive in the female reproductive tract, to be transmitted sexually in a way compatible with known risk factors, such as promiscuity and low socioeconomic status. Herpes viruses were also implicated in other malignant diseases, including Burkitt's lymphoma, Nasopharyngeal carcinoma, Marek's disease and the Lucké renal adenocarcinoma. HSV was recovered from cervical tumour cells.