Population-based screening for cancer: hope and hype

Abstract

Several important lessons have been learnt from our experiences in screening for various cancers. Screening programmes for cervical and colorectal cancers have had the greatest success, probably because these cancers are relatively homogenous, slow-growing, and have identifiable precursors that can be detected and removed; however, identifying the true obligate precursors of invasive disease remains a challenge. With regard to screening for breast cancer and for prostate cancer, which focus on early detection of invasive cancer, preferential detection of slower-growing, localized cancers has occurred, which has led to concerns about overdiagnosis and overtreatment; programmes for early detection of invasive lung cancers are emerging, and have faced similar challenges. A crucial consideration in screening for breast, prostate, and lung cancers is their remarkable phenotypic heterogeneity, ranging from indolent to highly aggressive. Efforts have been made to address the limitations of cancer-screening programmes, providing an opportunity for cross-disciplinary learning and further advancement of the science. Current innovations are aimed at identifying the individuals who are most likely to benefit from screening, increasing the yield of consequential cancers on screening and biopsy, and using molecular tests to improve our understanding of disease biology and to tailor treatment. We discuss each of these concepts and outline a dynamic framework for continuous improvements in the field of cancer screening.

Figure 1. Age-adjusted incidence rates of invasive cancers for which population-based screening is practiced in the USA.

Annual incidence rates in men (for prostate and colorectal cancers) and women (for cervical and uterine, breast and colorectal cancers) over the age of 50 years are shown for a 37‑year period (1975–2012), based on data from the Surveillance, Epidemiology, and End Results (SEER) registry. Approximate eras of widespread use of the respective screening tests are represented by black lines, with dotted regions representing initial periods of increasing dissemination of the tests following their introduction. The incidence rates of cervical cancer in women and colorectal cancers in both men and women have declined since the early‑to‑mid 1980s, probably owing to the screening-based detection and subsequent removal of cervical intraepithelial neoplasia and colonic polyps, respectively. On the other hand, the incidence rates of prostate cancer and breast cancer have increased over the same timeframe, probably owing to increased detection of localized cancers as a result of the widespread use of prostate-specific antigen (PSA)-based and mammography screening, respectively.

Figure 2. A framework for ongoing improvement of cancer-screening programmes.

We present a modified version of the screening cascade proposed by the High‑Value Care Task Force of American College of Physicians. Our recommendations for cancer-screening programmes focus on incorporation of key clinical questions at each step of the cascade, as well as components of the ‘feedback loop’ (areas to refine) — aspects of screening decision‑making that can be actively improved using outcomes from the corresponding step on the cascade. IDLE, indolent lesions of epithelial origin.