Chemotherapy — or not?
Gene-expression signature in early breast cancer, resistance testing over the disease course.
A considerable share of patients with early ER-positive, HER2-negative breast cancer gain nothing from chemotherapy — except its toxicity. Grading and Ki-67 help with this distinction only to a point. In an analysis of 1,652 cases, 118 of 449 patients with a Ki-67 above 20 percent were classified molecularly as low risk: more than a quarter of those in whom the conventional marker pointed the other way.
In the metastatic course, the question is a different one. Under endocrine therapy, resistance mutations arise for which agents now exist. They can be detected in plasma without taking tissue again. And because they emerge only under the pressure of treatment, the report on the primary tumour says nothing of them.
The gene-expression signature belongs at the start: after surgery and before the decision on adjuvant systemic therapy. It requires a positive oestrogen receptor and a negative HER2 status. It is validated for premenopausal and postmenopausal patients, at negative and at positive nodal status.
Resistance testing from plasma belongs where endocrine therapy fails or the first sign of it appears. Because the mutation profile changes under treatment, timing matters: a report from two years ago says little about the situation today.
Which test at which point?
That depends on the individual case. Call us, and we will work through the constellation together.