Debate continues on what is an adequate margin width to define a clear margin and whether there is a need to excise pectoral fascia or remove skin in breast conserving surgery. This study set out to provide answers to these questions.

1411 patients with invasive breast cancer were treated by breast conserving surgery and post-operative whole breast radiotherapy from January 2000 to December 2005. Distance from each margin to any in situ or invasive cancer was measured and recorded. If full thickness of breast tissue was removed no re excision of anterior and posterior margins was performed even if disease was <1 mm from a margin. Patients ≤50 years of age and those with anterior or posterior margins <1 mm to invasive cancer had a radiation boost. Median follow-up time was 6.4 years.

Local in breast tumour relapse (IBTR) occurred in 50 patients. The overall actuarial IBTR rate at 5 years was 2.2%. There was no difference in IBTR when comparing patients with radial margins of 1-5 mm or 5-10 mm. Anterior and posterior margins <1 mm or with ink on tumour cells were not associated with an increase in IBTR.

There is no justification for radial margins of greater than 1 mm. If the anterior or posterior margin is <1 mm and full thickness of breast tissue has been removed, then re excision of these margins is unnecessary if boost radiotherapy is delivered.