Molecular Subtypes of Breast Cancer
Although still in the early stages of research, molecular breast cancer subtypes may become useful in planning treatment and developing new therapies. Most studies divide breast cancer into four major molecular subtypes:
- Luminal A
- Luminal B
- Triple negative/basal-like
- HER2 type
These same subtypes also appear in ductal carcinoma in situ [
35-36].
Other less common molecular subtypes have also been described including normal breast-like, apocrine molecular type and claudin-low type. Breast cancers that do not fall into any of these subtypes are often listed as unclassified.
At this time, molecular subtypes are used only in research settings and are not a part of standard medical practice.
Prognosis and treatment decisions are guided by
tumor stage,
hormone receptor status and
HER2/neu status.
The complex profile of each subtype is determined using molecular and genetic information from tumor cells. However, some characteristics (including hormone receptor status, HER2/neu status and proliferation rate) can be used to roughly define the four major subtypes (see Figure 4.9 below). Much of what is known about the four subtypes is related to these characteristics that are already well understood.
Subtype: Luminal A,
These tumors tend to be: ER+ and/or PR+, HER2-, low Ki67, Prevalence: 42-59%
Subtype: Luminal B,
These tumors tend to be: ER+ and/or PR+, HER2+ (or HER2- with high Ki67),
Prevalence: 6-19%
Subtype: Triple negative/basal-like, These tumors tend to be: ER-, PR-, HER2-, cytokeratin 5/6 + and/or HER1+, Prevalence: 14-20%
Subtype: HER2+,
These tumors tend to be: ER-, PR-, HER2+,
Prevalence: 7-12%
*These are the most common profiles for each subtype. However, not all tumors within each subtype will have all these features.