B19
Ipsilateral breast tumour relapse: local recurrence versus new primary and the effect of whole breast radiotherapy on the rate of new primaries
Dorothy Gujral1, Georges Sumo1, John Owen2, Anita Ashton2, Judith Bliss3, Jo Haviland3, John Yarnold1
1Royal Marsden Hospital, Sutton, UK, 2Gloucestershire Oncology Centre, Cheltenham, UK, 3The Institute of Cancer Research, Sutton, UK
Background
The justification for partial breast radiotherapy (PBRT) after breast conservation surgery for early breast cancer includes an assumption that ipsilateral breast tumour relapses (IBTR) presenting outside the index quadrant are mostly new primary tumours (NP) that develop whether or not radiotherapy is given. We aim to test the hypothesis that whole breast radiotherapy (WBRT) is ineffective in preventing NP by comparing rates in irradiated and contralateral breasts after tumour excision and WBRT.
Method
A retrospective review was undertaken of 1410 women with breast cancer entered into a prospective randomised trial of radiotherapy fractionation involving annual clinical assessment to identify IBTR and contralateral breast cancer (CLBC). IBTR was classified into local recurrence (LR) or NP based on location and histology, and subdivided as definite or likely depending on the completeness of clinical data. Rates of ipsilateral NP and CLBC were compared over a 15-year period of follow-up. Due to the non-independence of the endpoints, complex statistical methods are required for formal comparison of event rates.
Results
At a median follow-up of 10 years, there were 150 documented cases of IBTR: 118 (79%) were definite or likely LR; 27 (18%) were definite or likely NP; and 5 (3%) could not be classified. There were 71 cases of CLBC. Results of an analysis which allows for the reporting of multiple events within an individual will be reported to formally compare event rates.
Conclusion
Despite uncertainty in some cases in classifying IBTR as LR or NP on clinical criteria, the absolute numbers of each event type appear to suggest that WBRT reduces the rate of ipsilateral NP tumours.
