Published: 20-03-2024 08:53 | Updated: 28-03-2024 15:16

New data indicate the international definition of triple-negative breast cancer should be revised

Photo: GettyImages.

Interesting Swedish data, where the definition of triple negative breast cancer (TNBC) differs from that used internationally, brings additional insights to on ongoing discussion in the scientific community. The study was presented at the 2023 European Society for Medical Oncology (ESMO) meeting and is now published in Lancet Regional Health- Europe.

The Swedish definition of TNBC differs from the international version in that it also includes tumors with low expression of the Estrogen Receptor (ER) biomarker, ie in 1-9% of tumor cells. Internationally, ER-low breast cancer is classified as hormone sensitive and treated different from TNBC patients. This is despite previous studies demonstrating that the majority of ER-low tumors are molecularly similar to ER-zero, the latter completely without expression of ER, and meta-analyses that show no survival benefit from endocrine therapy in ER-low tumors.

The Swedish population-based study included all women diagnosed with TNBC in Sweden during 2008-2020 using the National Quality Register for Breast Cancer. Patient and tumor characteristics, treatment and survival in patients with low ER expression was compared to patients with no ER tumor expression.

5 655 patients were identified and included in the study, and 560 patients (10%) were defined as ER-low and 5 095 (90%) as ER-zero. The data demonstrated there are only small differences in tumor characteristics, no differences in response to neoadjuvant chemotherapy and no significant differences in prognosis (see Reference).

Photo: Irma Fredriksson.

"The international cut-off for ER-positivity and thus the definition of TNBC as only completely ER-negative is now increasingly questioned. ER-low tumors behave like ER-zero tumors and should be treated as such. On the basis of real-world data, the Swedish cutoff for hormone receptor positivity appears to be more clinically relevant. A changed international definition would give patients with ER-low expressing breast cancer the same treatment options as in TNBC, within studies and in clinical routine.” says Dr. Irma Fredriksson who led the study.

The study was carried out in collaboration with MSD, within the framework of an established research collaboration between Karolinska Institutet and the pharmaceutical company.


Acs, B., Hartman, J., Sönmez, D., Lindman, H., Johansson, A.L.V., Fredriksson, I.  Lancet Regional Health- Europe, 2024, online ahead of print