Benefits of cancer screening

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There were favourable trends in the incidence, stage, survival and/or mortality of breast, cervical and colorectal cancer in the period 1994-2019, according to a report on the most up to date national data and trends, which has been published by the National Cancer Registry.

The NCRI said the data was consistent with improvements in early detection and outcomes, with clear evidence for additional or more recent benefits of screening.  There are three national cancer screening programmes in Ireland – BreastCheck, CervicalCheck and BowelScreen.

“Almost a third of cervical cancer cases and a quarter of female breast cancer cases diagnosed during 2017-2019 were detected as a result of screening. A smaller proportion of colorectal cancers were screen detected,” said the report.

“The introduction of a population-based screening programme would be expected to decrease incidence in cervical and colorectal cancers, but not breast cancer. The incidence trends seen in our report are consistent with this.  Screen-detected cancer cases were, on average, detected at a substantially earlier stage than other cases diagnosed at the same ages. Survival has improved for all three cancers, with the biggest improvements seen in the age-groups targeted by the national screening programmes. Death rates of all three cancers have fallen significantly. Decreases in the age-groups targeted for screening have been more substantial than the overall decreases for all three cancers.”

NCRI Director Professor Deirdre Murray said: “This is the first time that the NCRI has undertaken an in-depth analysis on those cancers that have an associated screening programme. Internationally, there is clear evidence that programmatic cancer screening improves cancer outcomes and saves lives. This report demonstrates that the trends in Ireland are consistent with these international findings which is reassuring for service users, providers and policy makers.”

Internationally, there is substantial evidence showing that the introduction of a screening programme results in ‘stage shift’ towards a greater proportion of Stage I and II among diagnosed cancers.

On average, there were 6,524 cases of breast, cervical and colorectal cancers diagnosed (6,490 excluding male breast cancers) and 1,834 deaths due to these cancer types (1,828 excluding male breast cancers) each year in Ireland over the period 2017-2019. Of these, approximately 25% of breast, 32% of cervical and 6% colorectal diagnoses were screen-detected.

Breast, cervical and colorectal cancers accounted for 27.0% of all invasive cancers (excluding non-melanoma skin cancers) diagnosed 2017-2019, and 19.9% of all deaths from malignant neoplasms 2017-2019. In women, these three cancers accounted for 43.7% of all invasive cancers diagnosed (excluding non-melanoma skin cancers) and 29.0% of deaths from malignant neoplasms over that time period

The overall incidence rate of female breast cancer has shown a statistically significant increase (by 1.7% per year) since 2014. However, this increase in part reflects increasing trends in age-groups above and below the screening age-range (50-69). The latter group shows no significant trend from 2009 onwards.  Of breast cancers in the screening age-group (50-69 years) who were identified through screening, 93% were stage I or II at diagnosis, compared to only 74% at stage I or II among other cases that presented at the same age.  Age-standardised five-year net survival from breast cancer has increased from 72% for female patients diagnosed 1994-1998 to 88% for those diagnosed 2014-2018. Increases in five-year survival have occurred in all age-groups, with the screening age-group (50-69 years) experiencing the greatest increase (from 74% to 94% over the same periods).  The overall mortality rate of female breast cancer has shown a statistically significant decrease (by on average 1.8% per year) since 1994. Significant decreases trends in mortality rates since 1994 have occurred in both the screening age-group (50-69 years, by 2.8% per year) and the pre-screening group.

 The overall incidence rate of cervical cancer has shown a statistically significant decrease (by 2.8% per year) since 2009. The incidence rate in the screening age group (25-60) has fluctuated, which the NCRI says would be expected, since screening was introduced.   Of cervical cancers in the screening age-group (25-60 years) who were identified through screening, 88% were stage I or II at diagnosis, compared to only 52% of other cases at that age. Five-year survival from cervical cancer has increased from 57% for patients diagnosed 1994-1998 to 65% for those diagnosed 2014-2018. Over the same periods, five-year survival for cervical cancers in those of screening age (25-60 years) has increased more markedly, from 66% to 79%.

The overall incidence rate of colorectal cancer in males has shown a statistically significant decreasing trend (by 2.5% per year) since 2012, while females have also shown a significant decreasing trend, albeit ongoing since 1994 (by 0.3% per year). Incidence rates in the screening age-group (60-69 years) have decreased significantly for males (by on average 0.6% per year) since 2009, but no significant trends in females of screening age (60-69 years) were identified.  Of colorectal cancers in the screening age-group (60-69 years) who were identified through screening, 62-64% of tumours were stage I or II at diagnosis compared to just 37-39% of other cases at that age.   Five-year survival from colorectal cancer has increased from 50% for patients diagnosed 1994-1998 to 66% for those diagnosed 2014-2018. Increases in five-year survival have occurred in all age-groups, with the screening age-group (60-69 years) experiencing the greatest increase (from 52% to 72% over the same periods).