How Genomic Tests for ‘Subtypes’ Help Target Treatment
Experts now recognize there are several different kinds of breast cancer – some of which are more aggressive than others. Genomic tests such as MammaPrint® and BluePrint® analyze which breast cancers have a higher chance of recurrence and, in addition, classify the cancer by its molecular subtype.
Some breast cancers are not aggressive, and are unlikely to come back once they have been treated. Many patients with nonaggressive breast cancers can avoid the potentially serious side effects of chemotherapy, and still have excellent outcomes.
Each breast cancer has a particular molecular profile that can help determine how the cancer is treated. Genomic tests identify the molecular subtype and thus guide which type of treatment will be most effective.
There are currently four generally recognized molecular subtypes of breast cancer:
1) Luminal A
2) Luminal B
3) Basal (also called triple-negative)
4) HER2 (also called ERBB2)
Each molecular subtype behaves differently, and this often guides treatment plans. It’s best to get tests like MammaPrint and BluePrint performed, so that you and your doctor can make the best treatment decisions.
Luminal A: These cancers are the most common breast cancer subtype at 50% – 60%. They have a good prognosis with a lower relapse rate than other subtypes. They are characterized with higher levels of estrogen receptors (ER) and treatment is mainly based on hormonal therapy.1
Luminal B: 15% – 20% of breast cancers are Luminal B. They have an increased expression of proliferation-related genes and have a higher recurrence rate and lower survival rates after relapse than Luminal-A. Studies have shown that they don’t respond as well to hormonal treatment as Luminal A, but have a better response to chemotherapy in a neoadjuvant (pre-surgery) setting.1
Basal: Basal-like cancer represent 8% to 37% of breast cancers and is aggressive with robust cluster of genes expressed in the basal or outer layer of the mammary gland. They are often called “triple negative” because most lack both estrogen and progesterone receptors on their cells and they don’t overproduce the HER2. These tumors are associated with shortest relapse-free and overall survival, but do have higher rates of response to presurgery chemotherapy.1,2
HER2-positive: These tumors account for 15-20% of breast cancers. They are characterized by a high expression of the HER2 gene (Human epidermal growth factor receptor-2). Without treatment, HER2-positive tumors have a poor prognosis. They have an increased resistance to hormonal treatments, but do respond to some chemotherapies.1
 Yersal O, Barutca S. World J Clin Oncol. 2014 Aug 10; 5(3): 412-424.
 Toft DJ, Cryns VL. Mol Endocrinol. 2011 Feb; 25(2): 199-211