395P - Receptor status heterogeneity during metastatic breast cancer treatment

Background

Systemic therapy options for patients with metastatic breast cancer (mBC) largely depend on the oestrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status. Prior studies have shown significant receptor discordance between the breast tumour and a metastatic site. We assessed the ER, PR, and HER2 discordance rates in patients with two biopsies during the metastatic disease course.

Methods

Patients diagnosed with mBC in ten Dutch hospitals between 2007 and 2020 were retrieved from the SONABRE Registry (NCT-03577197). Patients were identified if they had at least two biopsies at different time points during their mBC disease course. Last follow-up was collected in 2023. ER and PR positivity were defined as positive nuclear staining of ≥10%. HER2 positivity was defined as a positive in situ hybridization result or immunohistochemistry score of 3+.

Results

Among the 4,470 patients identified with mBC, 418 patients had two biopsies at different time points. Median follow-up since mBC diagnosis was 87 months, interquartile range: 54-122. ER, PR, HER2 and tumour subtype was available for both biopsies in 67%, 56%, 39%, and 37% of patients, respectively. ER, PR, HER2 and tumour subtype discordance was observed in 14%, 31%, 12% and 23% of patients, respectively. The highest discordance rates were observed in patients with HR+/HER2+ (55%, 46% changed to HR+/HER2-) and PR positive (46%) tumours.

Conclusions

HR+/HER2+ and PR positive tumours had the highest receptor discordance rates during the mBC disease course. The minority of patients with mBC underwent a second biopsy, yet, receptor status heterogeneity is frequent. Consequently, reassessing the receptor subtype may be beneficial to select appropriate targeted therapies.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

AstraZeneca, Novartis, Roche, Pfizer, Eli Lilly, Daiichi Sankyo, Gilead.

Disclosure

S. Geurts: Financial Interests, Institutional, Funding: Novartis BV, Roche, Pfizer, Eli Lilly, Daiichi Sankyo, Gilead, AstraZeneca. K. Hermans: Financial Interests, Institutional, Funding: Gilead, AstraZeneca. N. Teeuwen: Financial Interests, Institutional, Funding: Novartis BV, Roche, Pfizer, Eli Lilly, Daiichi Sankyo, Gilead, AstraZeneca. V. Tjan-Heijnen: Financial Interests, Personal and Institutional, Funding, and Advisory Board: Roche, Novartis, Pfizer, Eli Lilly; Financial Interests, Personal, Advisory Board: Accord Healthcare; Financial Interests, Institutional, Funding: AstraZeneca, Eisai, Daiichi Sankyo, Gilead. All other authors have declared no conflicts of interest.