The Cambridge post-mastectomy radiotherapy (C-PMRT) index: a practical tool for patient selection

Post mastectomy radiotherapy (PMRT) reduces loco-regional recurrence (LRR) and has been associated with survival benefit. It is recommended for patients with T3/T4 tumours and/or ⩾ 4 positive lymph nodes (LN). The role of PMRT in 1-3 positive LN and LN negative patients is contentious. The C-PMRT index has been designed for selecting PMRT patients, using independent prognostic factors for LRR. This study reports a 10 year experience using this index.

The C-PMRT index was constructed using the following prognostic factors (a) number of positive LN/lymphovascular invasion, (b) tumour size (c) margin status and (d) tumour grade. Patients were categorised as high (H) risk, intermediate (I) risk and low (L) risk. PMRT was recommended for H and I risk patients. The LRR, distant metastasis and overall survival (OS) rates were measured from the day of mastectomy.

From 1999 to 2009, 898 invasive breast cancers in 883 patients were treated by mastectomy (H: 323, I: 231 and L: 344). At a median follow up of 5.2 years, 4.7% (42/898) developed LRR. The 5-year actuarial LRR rates were 6%, 2% and 2% for the H, I and L risk groups, respectively. 1.6% (14/898) developed isolated LRR (H risk n = 4, I risk group n = 0 and L risk n = 10). The 5-year actuarial overall survival rates were 67%, 77% and 90% for H, I and L risk groups, respectively.

Based on published literature, one would have expected a higher LRR rate in the I risk group without adjuvant RT. We hypothesise that the I risk group LRR rates have been reduced to that of the L risk group by the addition of RT. Apart from LN status and tumour size, other prognostic factors should also be considered in selecting patients for PMRT. This pragmatic tool requires further validation.