(CSPOT37) Use of anthracyclines and trastuzumab in breast cancer patients with comorbid cardiovascular disease in Sweden: a cross-sectional study

Background: Anthracyclines and trastuzumab are highly effective breast cancer treatments, but known cardiotoxicities have discouraged their use in patients with existing cardiovascular disease. There are concerns that this may have led to some women receiving sub-optimal anti-cancer therapy. It is important to understand how these drugs are used in clinical practice to understand whether risks and benefits are being appropriately balanced.

Objectives: We aimed to assess the associations between history of cardiovascular disease and use of anthracyclines and trastuzumab in women diagnosed with non-metastatic breast cancer between 2010 and 2015 in Sweden.

Methods: We used linked data from Swedish registries, including the National Quality Register for Breast Cancer and the National Patient Register. Cardiovascular and other comorbidities present at breast cancer diagnosis were ascertained from hospital diagnoses and pharmacy drug dispensing records. Multivariable logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) for the association between prior cardiovascular disease and receipt of anthracyclines and trastuzumab (separately) in the first year of treatment, adjusted for key variables such as age, stage at diagnosis, measures of socio-economic status and comorbidities.

Results: 33,067 women had unilateral non-metastatic breast cancer in the study period, and 11,098 (33.6%) had a prior history of cardiovascular disease. Women with prior cardiovascular disease tended to be older, of lower socio-economic status, have more comorbidities and more advanced breast cancer at diagnosis. Among the 11,283 (34.1%) women who had any chemotherapy in the first year after diagnosis, 10,926 (96.8%) received anthracyclines, including 2,244 women with prior cardiovascular disease (20.4% of the women who had anthracyclines). Women with prior cardiovascular disease were substantially less likely to be offered anthracyclines both in crude (OR=0.41, 95% CI: 0.33-0.51, P< 0.001) and adjusted models (OR=0.60, 0.47-0.78, P< 0.001). Among the 29,432 women with known HER2 status, 4,003 (13.6%) had tumours that expressed HER2. Among these women, 1,137 (28.4%) had known history of cardiovascular disease, which was inversely associated with use of trastuzumab in the crude analysis (OR=0.36, 0.31-0.41, P< 0.001) and to a lesser extent in the adjusted one (OR=0.80, 0.66-0.97, P=0.024).

Conclusions: Anthracyclines and immunotherapy with trastuzumab were less likely to be offered to breast cancer patients with prior cardiovascular diseases, though a minority of women with cardiovascular diseases were treated with these drugs. Further studies may address the long-term cardiovascular health implications of these treatments.