The clinical relevance of various methods of classifying ipsilateral breast tumour recurrence as either true local recurrence or new primary

Purpose: Describes the relevance of –various classification methods for ipsilateral breast tumour recurrence (IBTR) as either true recurrence (TR) or new primary (NP) on both disease-specific survival (DSS) and distant metastasis-free survival (DMFS). Method: Two hundred and thirty-four of 4359 women undergoing breast-conserving therapy experienced IBTR. We compared the impact of four known classification methods and two newly created classification methods. Results: For three of the methods, a better DSS was observed for NP compared to TR with the hazard ratio (HR) ranging from 0.5 to 0.6. The new Twente method classification, comprising all classification criteria of three known methods, and the new Morphology method, using only morphological criteria, had the best HR and confidence interval with a HR 0.5 (95% CI 0.2–1.0) and a HR 0.5 (95% CI 0.3–1.1), respectively. For DMFS, the HR for NP compared to TR ranged from 0.6 to 0.9 for all six methods. The new Morphology method and the Twente method noted the best HR and confidence intervals with a HR 0.6 (95% CI 0.3–1.1) and a HR 0.6 (95% CI 0.4–1.2), respectively. Conclusion: IBTR classified as TR or NP has a prognostic value for both DSS and DMFS, but depends on the classification method used. Developing and validating a generally accepted form of classification are imperative for using TR and NP in clinical practice.