Background:
Breast cancer is the most common cancer diagnosed in Australian women, and the second leading cause of cancer death. There are limited data on how breast cancer treatment patterns have evolved over time, after accounting for guiding factors such as cancer stage and subtype. The BreastSurgANZ Quality Audit (BQA) is a prospective dataset that collects data on the treatment and care of early and locally advanced breast cancer patients seen by breast surgeons in Australia and New Zealand.
Methods:
Treatment data on 93,011 patients diagnosed between 2006-2019 was analysed for treatment patterns including primary surgery type (mastectomy versus breast conserving surgery), axillary surgery type, adjuvant chemotherapy, and adjuvant radiotherapy. Univariate and multivariate logistic regression was performed to estimate the association of treatment patterns with various factors including year of diagnosis, tumour characteristics, and mode of detection. Only the first cancer episode for each patient was included.
Results
The cases recorded within BQA were estimated to include 50.3% of all breast cancers diagnosed in Australia over the study period. The proportion of patients receiving selected treatments (including mastectomy, axillary lymph node dissection, and adjuvant chemotherapy) declined over time, after adjusting for other factors. Mastectomy (rather than breast conserving surgery) became less common, representing 34% of cases in 2006 and 31% of cases in 2019, with an adjusted odds ratio (OR) of 0.718 (95% CI 0.697, 0.844). Adjuvant chemotherapy showed a similar decrease from 49% to 37% of cases, and an OR of 0.742 (95% CI 0.662, 0.832). Treatment with radiotherapy following breast conserving surgery remained stable over the study period at 89%. Tumour features including larger size, increased lymph node involvement, non-luminal A subtype, bilaterality, and higher grade were all associated with more intensive treatment.
Conclusion
Treatment patterns in Australia have changed significantly over the period of 2006-2019, with a shift away from mastectomy and decreases in adjuvant chemotherapy, but no evident change to radiotherapy following breast conserving surgery. While it has some limitations, such as not including outcome data, the BQA dataset is a valuable resource that allows examination of how treatment practices for early stage breast cancer patients change over time in line with new evidence, as well as the effect of important tumour and personal characteristics.