Behaviour of breast cancer molecular subtypes through tumour progression

Introduction Breast cancer (BC) becomes more aggressive throughout disease progression. Clinical stage is correlated with patient outcome. We hypothesised that BC molecular subtypes are associated with a poor prognosis in advanced clinical stages. We analysed the distribution and behaviour of molecular subtypes at different BC tumour size and variation of molecular subtype in recurrent lesions. Patients and methods We studied 1647 consecutive patients with non-metastatic invasive and microinvasive (Tmi) BC treated from January 1997 to December 2007. Patients were categorised by tumour size and molecular subtype. A chi-square method was used for multiple group comparisons. Kaplan-Meier product limit method was used to calculate overall survival and disease-free survival. Results Median follow-up was 7.2 years. For patients with invasive BC the median age was 56 years. Four hundred and fifteen patients recurred and 225 died. Larger tumours were more frequently of triple-negative (TN) subtype than small ones or Tmi lesions. Any molecular subtype change from primary tumour to recurrent lesions is more likely to happen from a good prognosis to a subtype of worse prognosis than the opposite. Larger tumours of luminal A, luminal B and TN, but not HER2 subtype, are more likely to carry aggressive markers and to have worse outcomes than small ones. Conclusion We found accumulation of TN subtype, migration to a poor prognosis subtype and increasing aggressiveness of luminal and TN subtypes throughout tumour progression. Tumours belonging to the HER2 subtype behave aggressively regardless of the primary size.