Mar 06 2017
The use of Papanicolaou (Pap) tests for cervical cancer prevention and early detection has been an essential aspect of gynecological care in the United States since the 1950s. Recently Pap tests have been supplemented by the use of viral genotyping tests for the types of human papilloma virus (HPV) which cause essentially all cervical cancers as well as by the HPV vaccine (co-invented by Georgetown’s own Dr. Schlegel!). Given the huge decrease in cervical cancers due to the introduction of the Pap test, it is hard to remember that in the 1940s cervical cancer was a major cause of mortality for young women in the US – it is now only the 14th most frequent cancer in American women while still being a major driver of mortality in many parts of the world – globally it is the 4th most common female cancer and the 2nd most common in the developing world. Improved adoption of screening and vaccination practices are on their way to changing this picture. Since HPV also causes certain types of head and neck cancers in both men and women, HPV vaccines may play an even larger role in cancer prevention in the future.
An important note about cervical cancer: Recent work has shown that both the incidence and mortality rates and the disparities between these outcomes for black and white women are higher than had been previously estimated, particularly for older women, due to the inclusion of women who had had hysterectomies – which generally include removal of the cervix – in the denominator. There is still much work to be done, but the type of tools available for cervical cancer prevention and early detection would be a dream to researchers in other cancer fields!
Hepatocellular carcinoma (HCC) – the most common type of liver cancer – is generally the result of chronic infection with hepatitis B virus (HBV) or hepatitis C virus (HCV); a 2006 study led by the CDC estimated that 78% of cases worldwide can be attributed to these two viruses, which can also lead to a variety of other problems such as cirrhosis. Over the past couple of decades, the incidence of HCC has been increasing in the US, with approximately half of the extra cases between 1975 and 2007 being due to the increase of older individuals with chronic HCV. HCV was only discovered in 1989 and screening of donated blood and organs for this virus only became available in 1992. Since infected blood was a common source for HCV transmission before that time, the CDC recommends that all adults born between 1945 and 1965 be tested for HCV regardless of other risk factors, given that those individuals are five times as likely to be infected compared to other adults and an estimated 45%-85% of HCV-positive individuals are not aware of their status. A number of highly effective treatments for HCV now exist; the primary challenge right now is the high price of the drugs, which often leads to their use being limited to a subset of infected individuals, such as those who already have advanced liver disease.
The situation is somewhat simpler for HBV compared to HCV, as an effective vaccine exists, which is now part of the standard childhood vaccine schedule recommended by the CDC. Consequently the incidence of HCC can be expected to have a substantial drop over the next few decades. I mentioned in Part 1 of this series that I would not discuss the prevention of infectious diseases via vaccination in this series. When talking about cancer prevention though, I could not help but highlight the astounding fact that yes, there are vaccines against specific cancers!