Technological accretion in diagnostics: HPV testing and Pap testing in cervical cancer screening

This chapter follows the emergence of molecular HPV testing technologies and their application to cervical cancer screening in the USA. When HPV testing was first commercialised in the late 1980s, screening for cervical cancer had been a routine part of preventive healthcare for at least two decades, with testing conducted by cervical cytologists using the Pap smear test, a technology first developed in the 1910s. Many now predict that molecular HPV tests will eventually replace cervical cytology, bringing fundamental changes to the clinical infrastructure of screening in the process. However, at present these technologies not only co-exist but augment each other. This process of technological accretion has involved not only an accommodation with molecular technologies, but also the widespread adoption of novel cytology technologies: liquid-based cytology (LBC) and automated slide readers. This chapter explores the institutional factors that have shaped this contingent outcome. We begin by setting out the clinical context of cervical cancer screening. Cervical carcinoma is the fourth most common form of cancer in women, and is the cause of 7.5% of cancer deaths in women worldwide (IARC, 2012). These global statistics belie a grossly unequal disease burden: cervical cancer is now predominantly a disease of low- and middle-income countries, because since the 1960s both incidence and mortality rates have dropped dramatically in many developed countries. This is generally ascribed in large part to the introduction of screening programmes; cervical cancer screening (CCS) has become ubiquitous in the developed world with many countries running national programmes to ensure that women have the opportunity for regular screening. Statistics from the USA show a greater than 50% decline over 30 years in both incidence and mortality which are widely attributed to cervical cancer screening, although the disease still kills around 2.38 in 100,000 women in the USA (ACOG, 2012) . The decline in incidence and mortality is due primarily to that fact that screening identifies pre-invasive lesions which can be treated well before the possible onset of cancer (Saslow et al, 2012). Until recently cytology-based screening has relied on a technology developed in the first half of the twentieth century: the Pap smear. The traditional Pap smear involves scraping cells from the cervix and smearing them in a thin layer on a glass slide. The cells are then stained and examined under a microscope by a cytologist, to check for abnormalities. In the 1990s the traditional Pap began to be replaced by liquid-based cytology – a technique which involves placing the cells into preserving fluid and then filtering them to remove impurities prior to examination by microscope. However, even before LBC became routine, a more radical alternative technology was in development. In 1983 scientists provided strong evidence for an association between cervical cancer and human papilloma virus (HPV) when they cloned two carcinogenic HPV types (HPV 16 and 18), and soon thereafter companies began to develop HPV tests for use in cervical cancer screening.