Gene expression in breast cancer provides valuable biological information for better determining the diagnosis, treatment, risk of relapse and survival rate. However, the most common form of characterizing breast cancer is by histopathological techniques. This study, headed by Dr Aleix Prat, Head of the Translational Genomics Group at the Vall d'Hebron Institute of Oncology (VHIO) and an oncologist at the Breast Cancer Unit of the Vall d´Hebron University Hospital, focused on hormone-sensitive breast tumours known as luminals. The study compared data on tumours obtained by gene expression with histopathological data and proposes a new definition which improves the current classification of these tumours in routine clinical practice.
This finding, published recently in the Journal of Clinical Oncology, changes the current definition of these tumours, guaranteeing improved diagnosis by minimizing classification errors and hence improving the therapeutic approach and prognosis of patients with this breast cancer subtype.
Gene expression: the "digital fingerprint" of tumours
In any breast cancer case, it is essential to establish its molecular subtype. In recent years, gene expression has identified two major groups of hormone-sensitive tumours known as Luminal A and Luminal B. Treatment is based on this classification and therefore needs to be extremely precise. "Luminal A tumours have a good prognosis with hormone treatment, while Luminal B tumours have a less optimistic prognosis and in most cases require chemotherapy. The problem lies in the fact that the current method for defining these groups by histopathological data is not perfect, and we therefore need an additional parameter to help us yet further fine-tune the histopathological diagnosis of Luminal A and B tumours," explains Dr Aleix Prat, leader of the study.
At present, the way of defining luminal or hormone-sensitive tumours is by testing positive to hormone receptors and negative to HER2 expression. The difference between a Luminal A and Luminal B tumour is the amount of Ki-67 protein detected by the pathologist in the tumour cells. If the tumour has fewer than 14% Ki-67-positive cells, it is classified as Luminal A. The problem with this definition of subtype Luminal A is that ~30% of these tumours are actually shown as Luminal B by gene expression and hence have an unfavourable prognosis with hormone treatment alone.
A study offering diagnostic improvements