Original ResearchBreast cancer in young women and prognosis: How important are proliferation markers?

•Proliferation markers are highly expressed in young women with breast cancer.•Proliferation markers do not have a major prognostic impact in young women.•Ki-67 is only prognostic in young women with luminal progesterone receptor-positive (PR+) tumours.•The optimal prognostic cut-off for Ki-67 varies by age.•Age is an independent prognostic factor only in women with luminal B PR+ tumours.

AimCompared to middle-aged women, young women with breast cancer have a higher risk of systemic disease. We studied expression of proliferation markers in relation to age and subtype and their association with long-term prognosis.MethodsDistant disease-free survival (DDFS) was studied in 504 women aged <40 years and 383 women aged ≥40 years from a population-based cohort. Information on patient characteristics, treatment and follow-up was collected from medical records. Tissue microarrays were produced for analysis of oestrogen receptor, progesterone receptor (PR), Her2, Ki-67 and cyclins.ResultsYoung women with luminal tumours had significantly higher expression of Ki-67 and cyclins. Proliferation markers were prognostic only within this subtype. Ki-67 was a prognostic indicator only in young women with luminal PR+ tumours. The optimal cut-off for Ki-67 varied by age. High expression of cyclin E1 conferred a better DDFS in women aged <40 years with luminal PR− tumours (hazard ratio [HR] 0.47 [0.24-0.92]). Age <40 years was an independent risk factor of DDFS exclusively in women with luminal B PR+ tumours (HR 2.35 [1.22-4.50]). Young women with luminal B PR− tumours expressing low cyclin E1 had a six-fold risk of distant disease compared with luminal A (HR 6.21 [2.17-17.6]).ConclusionsThe higher expression of proliferation markers in young women does not have a strong impact on prognosis. Ki-67 is only prognostic in the subgroup of young women with luminal PR+ tumours. The only cyclin adding prognostic value beyond subtype is cyclin E1. Age is an independent prognostic factor only in women with luminal B PR+ tumours.