Haemoccult test properties according to type and number of positive slides in mass screening for colorectal cancer.

Despite encouraging results from recent studies, there is still no consensus to undertake mass screening using the Haemoccult test in the general population. The success of mass screening for colorectal cancer depends among other things on Haemoccult test properties. In on-going screening programmes, the Haemoccult test consists of six slides and a test is considered positive if at least one slide is coloured. The aim of this work was to study the influence of the type and number of positive slides on the Haemoccult test's positive predictive value and characteristics of screened lesions. This work focuses on 63,958 first tests in a mass screening programme in Calvados (France) among people aged 45-74 years. There was a linear relation between the positive predictive value for cancer or an adenoma larger than 1 cm and the number of positive slides (P < 10(-4)). The positive predictive value for cancer or large adenoma was significantly higher when 4-6 slides were positive (44.3%) than when only 1-3 were positive (19.1%) (P < 10(-4)). In this latter group, the subjects in whom tumours were detected were younger and had significantly less extensive cancers. Borderline tests (no slides positive and at least one slide with a blue coloration confined to the edges) had a positive predictive value for cancer or an adenoma larger than 1 cm no different to that of tests with 1-3 positive slides. Subjects with borderline results were markedly younger than the others and had less extensive cancers and rectal localisation more often than the others. Our results suggest that (1) increasing the number of positive slides required to declare a test positive leads to an increase in the positive predictive value but is not to be recommended because of the sensitivity of the test and (2) considering borderline Haemoccult tests as positive in on-going and future mass screening campaigns would allow an increase in the sensitivity of the test, especially for rectal cancer and low extensive tumours without any decrease in its positive predictive value.

Participants' characteristics in a French colorectal cancer mass screening campaign.

BACKGROUND: Participation by the target population is clearly a key element in the success of mass screening programs for colorectal cancer. In France, involvement of general practitioners in test distribution is essential to reach a satisfactory participation rate, but other forms of recruitment also have to be organized. The aim of this study was to determine the influence of demographic characteristics such as sex, age, and place of residence on the participation rate in a French mass screening according to different recruitment methods. METHODS: The Hemoccult IIR test was proposed in three consecutive ways: spontaneously by general practitioners and occupational doctors during appointments (phase 1), by postal invitation (phase 2), and finally by direct mailing of the test (phase 3). The target population consisted of 11,947 people between 45 and 74 years of age, living in a district of the French county of Calvados, between March 1991 and April 1993. RESULTS: The overall participation rate was 51.3%. Forty-nine percent of all the tests were done during phase 1, 31% during phase 2, and 20% during phase 3. The overall participation rate varied essentially according to the place of residence, from 65.5% in urban areas and 48.9% in intermediate areas to 27.7% in rural areas. The overall participation rate was also higher for females (57%) than for males (45%) and for those 60 years and older (53.9%) than for those below this age (49.2%). The proportion of tests done during phase 1 was lowest among the youngest and the oldest age groups (37.5% in the 45- to 49-year class and 45.2% in the 70- to 74-year class) and among people living in the rural environment (respectively 55.3%, 45.5%, and 35.9% in urban, intermediate, and rural areas). CONCLUSIONS: This study shows that place of residence strongly influences the global participation rate in mass screening for colorectal cancer in France, whereas sex and age have little influence. Recruitment methods complementary to distribution by general practitioners must be organized, especially for the youngest and oldest age groups (45-49 years and 70-74 years) and above all for people living in rural areas. The social, cultural, and psychological reasons for these differences remain to be investigated, with the aim of adapting mass screening strategies to the different population groups.