Benefits and harms of breast cancer screening revisited: a large, retrospective cross-sectional study quantifying treatment intensity in women with screen-detected versus non-screen-detected cancer in Australia and New Zealand

Objectives Non-mortality benefits of breast cancer screening are rarely considered in assessments of benefits versus harms. This study aims to estimate the rate of overdiagnosis in women with screen-detected breast cancer (SDBC) by allocating cases to either possibly overdiagnosed (POD) or not overdiagnosed categories and to compare treatment recommendations for surgery and adjuvant treatments by category, age at diagnosis and cancer stage.Methods and analysis Retrospective secondary analysis of 10 191 women diagnosed with breast cancer in Australia and New Zealand in 2018. Treatment recommendations for 5226 women with SDBC and 4965 women with non-SDBC (NSDBC) were collated and analysed. Descriptive statistics were used to calculate proportions and risk ratios (RRs).Results The POD rate was 15.8%. Screening detected 66.3% of stage 0 tumours, 59% of stage 1, 40% of stage 2 and 27.5% of stage 3 tumours. Women with SDBC were less likely than their NSDBC counterparts to receive chemotherapy (RR 0.60 Aus/0.53 NZ), immunotherapy (mostly human epidermal growth factor 2 receptor therapy) (RR 0.58 Aus/0.82 NZ), mastectomy (RR 0.55 Aus/0.63 NZ) and axillary lymph node dissection (RR 0.49 Aus/0.52 NZ), or to require both mastectomy and radiotherapy (RR 0.41 Aus/0.34 NZ). Less than 1% of POD women were recommended chemotherapy, 9.5% radiotherapy, 6.4% endocrine therapy, 2.2% mastectomy and 0.5% axillary lymph node dissection.Conclusions Women with SDBCs required less intensive treatment; rates of possible overtreatment of SDBCs are relatively low and may be minimised through multidisciplinary discussion and shared decision-making. Reduced treatment intensity should be considered when balancing the potential benefits and harms of screening.