Session Item

Describing nationwide trends and variation in radiotherapy (RT) use in the context of locoregional non-metastatic (M0) breast cancer treatment in the Netherlands from 2008 until 2019.

Women diagnosed with M0 breast cancer in 2008-2019 were selected from the population-based Netherlands Cancer Registry. Primary treatment was presented over time. Non-specified RT use was available in all study years. RT details were available from 2011. Use of whole breast irradiation (WBI) with boost/WBI without boost/partial breast irradiation (PBI) were presented in women who underwent breast conserving surgery (BCS). Multilevel logistic regression analyses were applied to identify variables associated with (1) post-BCS WBI with boost versus without, and (2) regional RT versus axillary lymph node dissection (ALND) in women with N+ disease.

During 2008-2019, 176,292 women were diagnosed with M0 breast cancer in the Netherlands. An increasing percentage received RT in 2008 (61%)–2016 (70%), caused by a shift from mastectomy to breast conserving therapy and increased post-mastectomy RT use (Fig 1A). After 2016, RT use slightly decreased to 67%, as women aged ≥70yrs more frequently received BCS without RT (Fig 1B/C). RT de-escalation was also observed by increased PBI use and decreased boost RT use following WBI (Fig 2). Older women (>75vs<50yrs OR:0.04, 95%CI:0.03-0.05) were less likely to receive boost RT, while women with N+ or higher grade disease (pN+ vs pN0 OR:1.46 95%CI:1.32-1.60 / grade III vs I OR:11.46, 95%CI:9.90-13.26) or residual tumour (focal R1 vs R0 resection OR:28.08, 95%CI:23.07-34.17) had an increased probability of receiving boost RT. Variation in boost RT was observed between regions of residence but could not be explained by hospital characteristics. In women with N+ disease, increased regional RT use (32% in 2011-61% in 2019) coincided decreased ALND use (76% in 2011-24% in 2019). Women aged >75yrs least often received regional treatment and were less likely to receive regional RT instead of ALND (>75vs<50yrs OR:0.68, 95%CI:0.95-0.78). Also, women with poorer WHO performance status, higher T-stage or grade, or >30 minutes travel time for RT less likely received regional RT instead of ALND, while women with lymph node micrometastases more likely received regional RT. N+ treatment varied between regions of residence (Southwest vs North OR:0.55, 95%CI:0.37-0.80) but not for hospital characteristics.

RT use in primary M0 breast cancer treatment increased until 2016 and slightly decreased afterwards. Clinical practice has de-escalated treatment as RT following BCS was more often omitted in older women, PBI use increased, and boost RT following post-BCS WBI strongly decreased. Boost RT varied for patient and disease characteristics and by region. N+ disease became frequently treated with regional RT instead of ALND, which use varied for women’s age, performance, disease characteristics, RT travel time and region of residence.