Screening status, tumour subtype and breast cancer survival: a national population-based analysis

Katie O’Brien, Linda Sharp (Institute of Health & Society, Newcastle University, Newcastle upon Tyne, UK), Therese Mooney (National Screening Service, Ireland) and Patricia Fitzpatrick (School of Public Health, Physiotherapy & Sports Science, University College Dublin and National Screening Service, Ireland) have published a paper comparing clinical characteristics and survival between women with screen-detected and non-screen-detected breast cancer. The women with non-screen-detected breast cancer can be categorised into three separate groups;

  1. Women with interval breast cancers (where the cancer is detected within 24 months after a negative/clear mammographic screening)
  2. Lapsed attenders of the screening programme
  3. Non-participants of the screening programme

Thus, there were two aims of this study – the first was to explore whether there were tumour and demographic differences between women with breast cancer diagnosed via mammography screening, women with interval breast cancers, lapsed attenders and non-participants of the screening programme.

The second aim was to explore whether there were survival differences among the groups, taking into account estimated lead time bias (the length of time between the detection of a disease through screening and its usual clinical/symptomatic presentation and diagnosis).

Figure: Lead time bias
By Mcstrother - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=15703636

Screening is expected to introduce stage shift so that more breast cancers are detected and treated at an earlier stage and when the disease hasn’t spread.

Subtype (HER2 over-expressing, triple negative), stage (III/IV), grade (poor), having comorbidities, area of deprivation, smoking status and age were associated with having interval cancer or of being a non-participant of the screening programme in the multivariable model.

After correcting for lead-time bias and adjusting for stage, subtype, grade and socio-demographic variables, there was no evidence of a difference in the relative hazard of death from breast cancer by screening status. Different stage distribution amongst the women with screen-detected and interval cancers, lapsed attenders and non-participants accounted for almost all of the survival differences between these groups.

It should be noted that for women diagnosed with breast cancer, five-year follow up is a relatively short time frame due to the high overall survival rate.

The article is published in Breast Cancer Research and Treatment (Springer) and is available for online reading here.

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