Tumour biomarker expression relative to age and molecular subtypes of invasive breast cancer

Background: Quantitative differences in biomarker expression relative to age and molecular subtypes have not been well documented in invasive breast cancer (IBCA). Methods: Oestrogen receptor (ER), progesterone receptor (PR), HER2, ki67, p53 and DNA ploidy was performed by image analysis in 162 consecutive IBCAs in women (≤40 years) and compared with women ≥50 years (100 cases). Molecular subtypes were defined by immunohistochemistry (IHC). Results: Among young women, tumours were frequently ER negative (P=0.01) with lower ER (P<0.00), PR (P=0.03), higher ki67 index (KI) (P=0.01) and p53 (P=0.00) compared with older women. Triple negative was more frequent among young women with frequent lymph node involvement compared with older women. Luminal B among young vs old women showed lower ER (67% vs 88%), PR (32% vs 52%), higher KI (48% vs 34%) and p53 (19% vs 7%). Linear regression model showed increasing KI (P<0.0001) and p53 (P=0.0003) according to the molecular subtypes. Survival difference among subtypes was demonstrated by multivariate analysis (P=0.0092) after adjusting for age, race, tumour size, grade and stage.Conclusion:We demonstrated significant differences in biomarker expression relative to age and molecular subtypes. Molecular subtype defined by IHC was an independent prognostic factor.