252P - Evolution of breast cancer biological subtypes between pre-treatment biopsy and residual disease after neoadjuvant therapy

Background

The reassessment of biomarkers: estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 (HER2) status is a standard procedure required in patients diagnosed with recurrent breast cancer (BC). The receptors conversion in residual disease (RD) after neoadjuvant therapy (NAT) is a phenomenon with unclear prognostic significance.

Methods

The clinicopathological characteristics and the pattern of receptors conversion were retrospectively analyzed in three main biological subtypes: luminal, HER2-positive and triple negative breast cancer (TNBC) in patients who underwent operation after NAT and had RD from January 2019 to December 2023. Only patients with biopsy and surgery performed at our institution with receptors determined in both specimens were included in the analysis.

Results

440 patients fulfilled inclusion criteria. In 152/440 patients (34.5%) with RD a switch of either ER/PR and/or HER2 status between the initial biopsy and the surgical specimen was detected. A total of 55/440 (12.5%) cases experienced a change in biological subtype with the following frequency: 14/287 (4.9%), 36/96 (37.5%), and 5/57 (8.8%) in originally luminal, HER2-positive and TNBC, respectively. HER2-positive and TNBC cases mainly switched to luminal tumors and luminal cases to HER2-positive cancers. Patients with HER2-positive BC at diagnosis were more likely to had a discordant biological subtype in post-NAT compared to luminal (difference by 32.6%, p<0.001) and TNBC (difference by 28.7%, p<0.001) whereas no significant difference was observed between TNBC and luminal (difference by 3.9%, p=0.268). Type of NAT (chemotherapy vs hormone therapy) in luminal cancers did not influence the pattern of subtype change.

Conclusions

One in 8 patients with early BC experienced a change in biological subtype between pre-NAT biopsy and the corresponding post-NAT surgical specimen. The discordance was the most pronounced in originally HER2-positive cases. Reassessment of biomarkers in early BC and adaptation of adjuvant therapy can be of value thus should be considered in future studies.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Katarzyna Pogoda.

Funding

Has not received any funding.

Disclosure

K. Pogoda: Financial Interests, Personal, Invited Speaker: AstraZeneca, Roche, Gilead, Novartis, Eli Lilly, Pfizer; Financial Interests, Personal, Advisory Board: Sandoz, AstraZeneca; Financial Interests, Personal, Full or part-time Employment, Assistant Professor: Maria Sklodowska-Curie National Research Institute of Oncology, Warsaw, Poland; Financial Interests, Personal and Institutional, Other, SI: Novartis, Roche, Eli Lilly, AstraZeneca; Non-Financial Interests, Other, Breast Cancer Group - Steering Committee Member, Quality of Life Group: EORTC; Non-Financial Interests, Member: Polish Society of Clinical Oncology, Polish Society of Oncology. W. Olszewski: Financial Interests, Personal, Invited Speaker: AstraZeneca, Gilead, Roche, MSD. A. Niwinska: Financial Interests, Personal, Invited Speaker: Novartis, Gilead. A. Balata: Financial Interests, Personal, Invited Speaker: Novartis. M. Meluch: Financial Interests, Personal, Invited Speaker: Novartis, Lilly, AstraZeneca. A. Mlodzinska: Financial Interests, Personal, Invited Speaker: Novartis, AstraZeneca. Z. Nowecki: Financial Interests, Personal, Invited Speaker: Gilead. All other authors have declared no conflicts of interest.