St Gallen molecular subtypes in screening-detected and symptomatic breast cancer in a prospective cohort with long-term follow-up

Background: Diagnosis by screening mammography is considered an independent positive prognostic factor, although the data are not fully in agreement. The aim of the study was to explore whether the mode of detection (screening-detected versus symptomatic) adds prognostic information to the St Gallen molecular subtypes of primary breast cancer, in terms of 10-year cumulative breast cancer mortality (BCM). Methods: A prospective cohort of patients with primary breast cancer, who had regularly been invited to screening mammography, were included. Tissue microarrays were constructed from primary tumours and lymph node metastases, and evaluated by two independent pathologists. Primary tumours and lymph node metastases were classified into St Gallen molecular subtypes. Cause of death was retrieved from the Central Statistics Office. Results: A total of 434 patients with primary breast cancer were included in the study. Some 370primary tumours and 111 lymph node metastases were classified into St Gallen molecular subtypes. The luminal A-like subtype was more common among the screening-detected primary tumours (P=0.035) and corresponding lymph node metastases (P=0.114) than among symptomatic cancers. Patients with screening-detected tumours had a lower BCM (P=0.017), and for those diagnosed with luminal A-like tumours the 10-year cumulative BCM was 3 per cent. For patients with luminal A-like lymph node metastases, there was no BCM. In a stepwise multivariable analysis, the prognostic information yielded by screening detection was hampered by stage and tumour biology. Conclusion: The prognosis was excellent for patients within the screening programme who were diagnosed with a luminal A-like primary tumour and/or lymph node metastases. Stage, molecular pathology and mode of detection help to define patients at low risk of death from breast cancer.