**3.1 Luminal A and luminal B traits**

High expression of ER-related genes, low expression of the HER2 cluster of genes, and low expression of proliferation-related genes are the two main characters of Luminal A tumors. This kind has the best prognosis of all breast cancer subtypes. Whereas luminal B tumors have relatively lower (although still present) expression of ER-related genes, variable expression of the HER2 cluster, and higher expression of the proliferation cluster.

Luminal B tumors carry a worse prognosis than luminal A tumors. Unfortunately, this subtype has high probability of recurrence.
