[The quality indicator 'tumour positive surgical margin following breast-conserving surgery' does not provide transparent insight into care].

OBJECTIVE

To determine whether the quality indicator 'tumour positive surgical margin following breast-conserving surgery, consistently measured the quality of breast-cancer surgery independently of the different definitions used and differences in case mix, taking statistical random variation into account.

DESIGN

Descriptive study.

METHODS

Data was collected from 762 patients who underwent breast-conserving surgery for invasive or in situ carcinoma of the breast, in the period 1 July 2007 - 30 June 2008 in 1 of the 9 hospitals in the region of the Comprehensive Cancer Centre West in the Netherlands. We compared 3 definitions for 'tumour positive surgical margin': the one used by the Health Care Inspectorate, the one used by the organisation 'Zichtbare Zorg' ('transparent care') and the percentage of re-resection. For case mix correction we identified risk factors for tumour margin positivity with logistic regression. The results were presented in a funnel plot, using 95% confidence interval (CI) around the national standard of 20%.

RESULTS

Depending on the definition used, the tumour positive surgical margin rate of the total group varied from 11 to 21%. Individual hospital rates varied by up to 19%. In situ carcinoma was associated with higher tumour positive surgical margin rates. Results differed significantly between hospitals for all 3 definitions. However, the funnel plot showed that results for most hospitals fell within the 95% CI of the standard. Whether a hospital fell within the 95% CI of the standard depended upon on the definition used and case mix correction.

CONCLUSION

The lack of a single definition for the quality indicator 'tumour positive surgical margin following breast-conserving surgery' and the lack of case-mix correction undermine the validity of the indicator. Standardisation of definitions, uniform registration and the use of funnel plots can provide a more transparent insight into the quality of care.