An analysis of 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 tumours with low expression of the Oestrogen Receptor (ER) biomarker, ie in 1–9% of tumour cells. Internationally, ER-low breast cancer is classified as hormone-sensitive and treated differently from TNBC patients. This is despite previous studies demonstrating that the majority of ER-low tumours 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 tumours.
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 tumour characteristics, treatment and survival in patients with low ER expression was compared to patients with no ER tumour expression.
The study identified and included 5655, and 560 patients (10%) were defined as ER-low and 5095 (90%) as ER-zero. The data demonstrated there are only small differences in tumour characteristics, no differences in response to neoadjuvant chemotherapy and no significant differences in prognosis.
“The international cut-off for ER-positivity and thus the definition of TNBC as only completely ER-negative is now increasingly questioned. ER-low tumours behave like ER-zero tumours 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 study leader Dr Irma Fredriksson.
The study was carried out in collaboration with the pharmaceutical company MSD.
Source: Karolinska Institutet
